Detector for Theft Prevention

The present invention relates to a detector for theft prevention comprising a box attached in contact with an object of theft prevention, and a switch attached to this box for detecting whether it has been detached from the object of theft prevention.

A theft preventive device comprising such a detector for theft prevention is used in contact with an object of theft prevention such as a commodity displayed in a shop, for example; The detector for theft prevention detects whether the theft preventive device has been detached from the object of theft prevention, and sounds an alarm.

As shown in FIG. 25, for example, a theft preventive device 100 is mounted in a case 101 to protect, from shoplifting, an object of theft prevention E such as a compact disk. The object of theft prevention E is inserted into the case 101 to contact the theft preventive device 100 (see, for example, Utility Model Application No. 3-11054 filed by Applicant).

A switch is provided for the theft preventive device as a detector for theft prevention to detect whether the theft preventive device has been detached from the object of theft prevention then. The switch has a pivotable operated portion biased to return to a position projected from a contact surface of the object of theft prevention. However, as shown in FIG. 26, the conventional operated portion can pivot only to one side from the projected position.

In the figure, 3' denotes a conventional switch having an operated portion 3a', and 102 denotes an alarm generator.

Since the conventional operated portion is pivotable only to one side from the projected position, the object of theft prevention cannot be moved in a direction that pivots the operated portion in a direction other than that direction.

Thus, when inserting the object of theft prevention E into the case 101, the object of theft prevention E is moved in a direction f1 as shown in FIG. 26. When removing the object of theft prevention from the case 101, the object of theft prevention E is moved in a direction f2. If the object of theft prevention E has an uneven contact surface (lower surface), the operated portion 3a' is caught on the unevenness when the object of theft prevention E is moved out of the case 101. Thus, the object of theft prevention E cannot be taken out. When an attempt is made to take out the object of theft prevention E forcibly, the operated portion 3a' could be damaged inadvertently.

An object of the present invention is to provide a detector for theft prevention that eliminates the drawbacks of the prior art noted above.

More particularly, the invention intends to provide a detector for theft prevention operable properly with regard to various directions of movement of an object of theft prevention, for example.

Furthermore, the invention intends to provide a detector for theft prevention having little chance of malfunction, capable of reliably detecting whether a theft preventive device has been detached or not, and having a high yield of manufacture.

A detector for theft prevention according to the present invention comprises a box attached in contact with an object of theft prevention, and a switch provided for this box for detecting whether it is detached from the object of theft prevention, the detector for theft prevention being characterized in that the switch provided for the box has a pivotable operated portion biased to return to a position projecting from a surface contacting the object of theft prevention, the operated portion being pivotable in a plurality of directions including at least two opposite directions.

With this construction, the operated portion is pivotable in a plurality of directions including at least two opposite directions. Even when the object of theft prevention moves in two opposite directions (e.g. in directions e1, e2 in FIG. 21), the operated portion pivots in accordance with pushed states (moving states) of the object of theft prevention.

Consequently, since the operated potion pivots in accordance with pushed states (moving states) of the object of theft prevention, the detector for theft prevention is properly operable for movements in varied directions of the object of theft prevention.

The contact surface may have a plurality of projections surrounding the operated portion to extend into the object of theft prevention

With this construction, where the theftobject of theft prevention preventive device is attached to an object of theft prevention such as a cardboard box, the plurality of projections surrounding the operated portion on the contact surface with the object of theft prevention am extended into the object of theft prevention. Thus, it is possible to detect a preliminary stealing act to insert a thin plate-like foreign object such as a ruler between the theft preventive device and object of theft prevention in order not to allow the operated portion to project from the contact surface. That is, when a thin plate-like foreign object is inserted between the theft preventive device and object of theft prevention, the foreign object ride on the plurality of projections, whereby the operated portion projects from the contact surface.

Consequently, since it is possible to detect a preliminary stealing act to insert a foreign object in order not to allow the operated portion to project from the contact surface, the theft prevention detector can positively detect whether the object of theft prevention is removed or not.

The box of the theft prevention detector of this invention may have receiver means for receiving a medium of information communication transmitted from a transmitter installed in a predetermined position, and an alarm sound output means for outputting an alarm sound based on detection information from the receiver means.

This construction is effective to detect a theft with increased reliability by means of the alarm sound.

It is preferable that the alarm sound output means does not send the medium for information communication transmitted from the transmitter.

With this construction, when the alarm sound output means operates to sound the alarm, it does not send the same medium as the medium for information communication transmitted from the transmitter installed in a predetermined location. Thus, even where theft preventive devices are disposed close to one another, the operation of the alarm sound output means does not cause malfunctioning of the receiver means of the other theft preventive devices.

Consequently, since the operation of the alarm sound output means does not cause malfunctioning of the receiver means of the other theft preventive devices, malfunctioning of the theft preventive devices is avoided to promote reliability of the theft preventive devices.

Further, the alarm sound output means may comprise a piezoelectric buzzer.

With this construction, since a piezoelectric buzzer is used as the alarm sound output means, the alarm sound output means may be formed thin and lightweight.

Consequently, the theft preventive device may be formed thin and lightweight.

Further, the box may have a battery for supplying electricity to the alarm sound output means and the alarm sound output means opposed to each other therein, and a plate-like terminal unit having a terminal connected to an electrode of the battery and a terminal connected to an electrode of the alarm sound output means is provided between the battery and the alarm sound output means.

In this construction, the battery (button type or coin type) and piezoelectric buzzer are opposed to each other, and a plate-like terminal unit having a terminal connected to an electrode of the battery and a terminal connected to an electrode of the piezoelectric buzzer is provided between the battery and piezoelectric buzzer. Thus, three types of flat components (battery, piezoelectric buzzer and terminal unit) are arranged in superposition within the box.

Consequently, the theft prevention apparatus may be formed very thin.

Further, the alarm sound output means may output an intermittent sound as alarm sound.

This construction facilitates recognition of the alarm sound of the theft preventive device, and reduces power consumption of the theft preventive device, there by promoting efficiency of the theft preventive device.

Consequently, shop assistants and the like recognizes the alarm sound with ease. Power consumption of the theft preventive device is less than where the alarm sound is outputted any time.

The box may have sound release openings formed in a side surface thereof for releasing the alarm sound outputted from the alarm sound output means outside said box.

With this construction, the alarm sound outputted from the alarm sound output means is released through the openings in the side surface of the box. The alarm sound release openings are difficult to block up, compared with the case where such openings are formed in a front surface or bottom surface of the box. That is, when the theft preventive device is formed thin, the side surfaces of the box have a smaller width than the front surface and bottom surface. If the openings were formed in the front surface or bottom surface of the box, it would be possible to block up the openings easily with fingers or the like (such an act is taken to stifle the alarm sound). However, the openings are difficult to block up by providing the openings in the side surface of the box.

Consequently, it is now possible to prevent effectively a preliminary stealing act to take the object of theft prevention outside the shop, with fingers blocking up the openings to suppress the alarm sound.

The box may have a shield wall mounted therein for shielding components in the box against exposure through the openings.

With this construction, since the shield wall is provided to shield components in the box against exposure through the openings, the shield can bar entry of a foreign object inserted through an opening into the box. The alarm sound generated in the box is guided round the shield wall to the openings to be released outside the box.

Consequently, it is now possible to prevent effectively a preliminary stealing act to destroy the components in the box by inserting a foreign object through an opening.

Further, the present invention may be modified such that the receiver means comprises a resonance antenna for a theft preventive device for outputting a signal to operate the alarm means upon receipt of the electric wave from the transmitter, and has a coil, a capacitor and a resistor in parallel connection.

With this construction, the resistor is connected in parallel to the coil and capacitor already in parallel connection. This resonance antenna has what is known as Q-value of a resonator lowered, whereby the resonance antenna has a reduced frequency selectivity. Thus, the reception sensitivity of the resonance antenna is little variable with variations in resonance frequency due to variations in circuit constant caused by variations in the coil and capacitor.

With this construction, therefore, the reception sensitivity of the resonance antenna is little variable with variations in resonance frequency. This minimizes variations in reception sensitivity occurring with different resonance antennas, thereby to promote yield in the manufacture of resonance antennas for use in theft preventive devices.

FIG. 1 is a schematic view of a theft preventive device in an embodiment of the present invention,

FIGS. 2(a), (b) are explanatory views of outward appearances of the theft preventive device of FIG. 1,

FIG. 3 is an explanatory perspective view of a bottom case component in the embodiment of FIG. 1,

FIG. 4 is an explanatory perspective view of top case components in the embodiment of FIG. 1,

FIG. 5 is a plan view of the top case in the embodiment of FIG. 1, FIGS. 6(a), (b) are explanatory views of a switch in the embodiment of FIG. 1,

FIGS. 7(a), (b) are sectional side views of the switch in the embodiment of FIG. 1,

FIGS. 8(a), (b) are explanatory views of outward appearances of a speaker housing in the embodiment of FIG. 1,

FIGS. 9(a), (b) are explanatory views of outward appearances of a terminal unit in the embodiment of FIG. 1,

FIG. 10 is a perspective view of an LED window in the embodiment of FIG. 1,

FIGS. 11(a), (b) are explanatory views of outward appearances of a jack unit the embodiment of FIG. 1,

FIGS. 12(a), (b) are explanatory views of a set button pin in the embodiment of FIG. 1,

FIG. 13 is an explanatory view of the jack unit in the embodiment of FIG. 1,

FIG. 14 is a perspective view of a principal portion of the embodiment of FIG. 1,

FIG. 15 is an explanatory view of an outward appearance of a slider in the embodiment of FIG. 1,

FIGS. 16(a), (b) are sectional views of the principal portion of the embodiment of FIG. 1,

FIGS. 17(a), (b) are sectional views of the principal portion of the embodiment of FIG. 1,

FIGS. 18(a), (b) are sectional views of the principal portion of the embodiment of FIG. 1,

FIG. 19 is a view of an outward appearance of a key in the embodiment of FIG. 1,

FIG. 20 is a perspective view of an outward appearance of a transmitter in the embodiment of FIG. 1,

FIG. 21 is an explanatory view of operation of the switch in the embodiment of FIG. 1,

FIG. 22 is an enlarged view of a coil in the embodiment of FIG. 1,

FIG. 23 is an explanatory view of an outward appearance of a theft preventive device in another embodiment,

FIGS. 24(a), (b), are explanatory views of outward appearances of a theft preventive device in a further embodiment,

FIG. 25 is a perspective view of a theft preventive device known in the art, and

FIG. 26 is an explanatory view of operation of a switch in the in the known theft preventive device.

An embodiment of the present invention will be described hereinafter with reference to the drawings.

As shown in FIG. 2, a sensor tag 1 acting as a theft preventive device includes a box 2 attached with a top surface (contact surface) thereof contacting an object of theft prevention E (FIGS. 25 & 26). FIG. 2(a) is a perspective view of the sensor tag 1, and FIG. 2(b) shows a rear surface 2n of the sensor tag 1.

The sensor tag 1 includes a switch 3 having a pivotable operated potion 3a biased to a projection position projected from the contact surface 2c. This switch 3 is turned ON/OFF by pivotal movement of the operated portion 3a. Consequently, the operated portion 3a of the switch 3 pivots by presence or absence of the object of theft prevention E to turn the switch 3 ON/OFF, to detect whether the sensor tag 1 has been detached from the object of theft prevention or not.

As shown in FIG. 1, the box 2 of sensor tag 1 contains an LED lamp (chip LED) 20 acting as a light emitting device; a piezoelectric buzzer 21; a resonance antenna 22 including a cell E, a capacitor C and a resistor R; an antenna input circuit 23 for outputting a reception signal when the resonance antenna 22 is in signal receiving state; a switch input circuit 24 for outputting OFF signal indicating OFF state of switch 3; a switching circuit 25 for outputting a control signal upon receipt of the reception signal from the antenna input circuit 23 or OFF signal from the switch input circuit 24; a generating circuit 26 which starts generating pulses upon input of the control signal from the switching circuit 25; a counter 27 which starts counting the pulses generated by the generating circuit 26 upon input of the control signal from the switching circuit 25, and outputs a count completion signal when the count exceeds a predetermined number; a latch circuit 28 responsive to input of the count completion signal to maintain switching circuit 25 in the state of receiving the above reception signal or OFF signal; a buzzer/LED driver 29 acting as a drive device to light the LED lamp 20 and sound the piezoelectric buzzer 21 upon input of the count completion signal of counter 27; a flat battery (button type or coin type) V for supplying power to the respective circuits in the box 2; and a power supply switch 6 for turning on and off the power supply from the battery V to the circuits.

In the circuit having the above construction, the piezoelectric buzzer 21 mounted in the box 2 sounds when, with the power supply switch 6 turned on, the switch 3 is turn off, or the sensor tag 1 is passed through a position where a pair of panel-like transmitters O as shown in FIG. 20 are installed at opposite sides of an entrance of a shop. One of the panel-like transmitters O may be installed at one side of the entrance, or on a floor of the entrance.

In FIG. 2, 10 denotes openings formed in a side surface 2n of the box 2 for releasing the sound of the piezoelectric buzzer 21 outwardly of the box 2.

The resonance antenna 22 has its reception sensitivity adjusted beforehand according to an expected spacing with which the pair of transmitters O are installed.

The adjustment of reception sensitivity can be carded out in two ways.

The reception sensitivity of resonance antenna 22 increases linearly with an increase in the resistance value of resistor R. Accordingly, one of the two methods is carried out by appropriately changing the resistor R to one having a suitable resistance value.

When the resistance value of the resistor is changed, Q value of the resonance antenna changes with the resistance value, and the reception sensitivity of the resonance antenna changes with it.

On the other hand, the resonance frequency of the resonance antenna does not change even if the resistance value of the resistor is changed. Thus, the change of reception sensitivity by a change of resonance frequency need not be taken into account.

In adjusting the reception sensitivity of the resonance antenna, it is unnecessary to consider a change in reception sensitivity due to a change in resonance frequency. The reception sensitivity of the resonance antenna can, therefore, be adjusted easily.

The coil L has a drum type core L1 as shown in FIG. 22. The reception sensitivity of resonance antenna 22 increases linearly with an increase in flange diameter d of drum type core L1. The other method is carded out by using a core having a suitable flange diameter d. Even if flange diameter d is changed, the inductance of coil L should be maintained substantially fixed.

When the flange diameter of the drum type core of the coil is varied, the convergence effect of magnetic flux by the coil changes, which in turn changes the reception sensitivity of the resonance antenna.

On the other hand, the resonance frequency of the resonance antenna does not change with a change in the above flange diameter if the inductance value of the coil is fixed. Accordingly, a change in reception sensitivity due to a change in resonance frequency need not be considered.

Thus, in adjusting the reception sensitivity of the resonance antenna, a change in reception sensitivity due to a change in resonance frequency need not be considered. The reception sensitivity of the resonance antenna can be adjusted easily.

Next, a process for causing the piezoelectric buzzer 21 to begin to sound will be described briefly.

The sensor tag 1 is attached to object of theft prevention E, with the switch 3 turned ON to set in operative state (to turn on the switch 6). When the sensor tag is detached from the object of theft prevention E, the switch 3 becomes OFF. The switch input circuit 24 detects the OFF state.

Upon detection of the OFF state of switch 3, the switch input circuit 24 outputs the OFF signal to the switching circuit 25.

While the OFF signal is inputted from the switch input circuit 24, the switching circuit 25 sends the control signal to the generating circuit 26 and counter 27. While the control signal is received, the generating circuit 26 generates pulses, and the counter 27 counts the pulses generated by the generating circuit 26. When the control signal stops, the generating circuit 26 stops generating pulses, and the counter 27 stops counting and resets a pulse count.

Each time a predetermined count of pulses is reached, the counter 27 sends one pulse signal as a count completion signal to the latch circuit 28 and buzzer/LED driver 29.

While this count completion signal is received, the buzzer/LED driver 29 sounds the piezoelectric buzzer 21, and flashes the LED lamp 20.

On the other hand, the latch circuit 28 receives the count completion signal from the counter 27, and maintains the switching circuit 25 in the state of receiving the above OFF signal. The switching circuit 25 thereby continues sending the control signal to the generating circuit 26 and counter 27.

In other words, the buzzer/LED driver 29 sounds the piezoelectric buzzer 21 and lights the LED lamp 20 after the switching circuit 25 receives the OFF signal and the counter 27 completes counting up to the predetermined count. Thus, unless the OFF signal is continuously received over a fixed time, the piezoelectric buzzer 21 and LED lamp 20 remain out of operation. The prevents malfunctioning due to noise or the like.

The switching circuit 25 continues sending the control signal once the counter 27 outputs the count completion signal, regardless of presence or absence of the OFF signal from the wire unit input circuit 24. As a result, until the power supply switch 6 is turned off, the piezoelectric buzzer 21 continues outputting intermittent sound synchronously with the count completion signal from the counter 27, and the LED lamp 20 continues flashing synchronously with the count completion signal from the counter 27.

On the other hand, when the sensor tag 1 passes through a position where the transmitters O are installed, the resonance antenna 22 generates an electromotive force with an electric wave from the transmitters O. The antenna input circuit 23 detects the electromotive force, and outputs the reception signal to the switching circuit 25.

The operation of each circuit after the switching circuit 25 receives the reception signal is the same as when the above-mentioned switch 3 becomes OFF state, and will not be described again.

Thus, the resonance antenna 22 acts as a reception device for receiving a medium (electric wave) of information communication sent from the transmitters installed in a particular location. The piezoelectric buzzer 21 acts as an alarm sound output device to output an alarm sound based on reception information of the reception device (resonance antenna 22), but not to transit the medium (electric wave) of information communication sent from the transmitters O installed in the particular location.

The antenna input circuit 23, switching circuit 25, generating circuit 26, counter 27, latch circuit 28, buzzer/LED driver 29, LED lamp 20 and piezoelectric buzzer 21 act as an alarm device A operable upon receipt of the signal from the resonance antenna 22.

The construction and operation of each component will be described hereinafter.

As shown in FIGS. 3 and 4, the box 2 includes a bottom case 2a and a top ease 2b.

The bottom case 2a has a circuit board 30 carrying the switch 3, LED lamp 20, antenna 22 and various electronic components, a jack unit 4, a terminal 31 for plus electrode connection of battery V, and the battery V.

The top case 2b has, assembled thereto, the piezoelectric buzzer 21 formed of a piezoelectric vibration plate 21a, a speaker housing 32 and a terminal unit 33, an LED window (light window) 34 for releasing light from the LED lamp 20, and a slider 5. The sensor tag 1 shown in FIG. 2 is formed by joining the bottom case 2a and top case 2b by ultrasonic welding.

As shown in FIGS. 6 and 7, the switch 3 includes a box-like frame 3A formed of a non-conductive material such as a resin to define an open side; the substantially triangular operated portion 3a with one end thereof projecting upwardly of the contact surface; a substantially C-shaped first terminal plate 3b formed of metal and attached to the frame 3A to dose the opening; a second terminal plate 3c formed of metal and attached to an inner surface of the frame 3A; and a coil spring 3d acting as an elastic device supported on a boss defined by the frame 3A to be pivotable about a cross axis P. The operated portion 3a is held between the frame 3A and coil spring 3d to be pivotable in two opposite directions e1, e2 and biased to projection position w projecting from the upper surface of the frame 3A by opposite end portions of coil spring 3d extending from a middle portion q thereof.

The operated portion 3a projects from the contact surface 2c when the switch 3 is initially mounted in the box 2.

Further, the coil spring 3d acts as a connection terminal for connecting and disconnecting the first terminal plate 3b and second terminal plate 3c of switch 3. That is, the middle portion q of coil spring 3d constantly is in elastic contact with the first terminal plate 3b. When the operated portion 3a pushes down an end r of coil spring 3d, the end r of coil spring 3d moves into contact with the terminal plate 3c.

The operated portion 3a is pivotable in the two opposite direction e1, e2. Even if the object of theft prevention E moves in the two opposite directions e1, e2 as shown in FIG. 7, the operated portion 3a can operate the switch 3 properly in response to the movement of the object of theft prevention E.

FIG. 6(a) is a perspective view of switch 3, and (b) is a view showing a circuit construction of switch 3. FIGS. 7(a), (b) are sectional side views of switch 3.

The speaker housing 32 (FIG. 8) has, press fit therein, the piezoelectric vibration plate 21a and the terminal unit 33 shown in FIG. 9. The sound generated from the piezoelectric vibration plate 21a is released through the openings 32a to the outside.

In the drawings, 32b denotes a shielding wall for shielding the components in the box 2 against exposure to the outside through the openings 10, i.e. for preventing entry of foreign matters through the openings 10.

As shown in FIG. 9, the terminal unit 33 has terminals 33a, 33b connected to electrodes (+, -) of the piezoelectric vibration plate 21a when press fit in the speaker housing 32, and a terminal 33c connected to a minus electrode of battery V when the bottom case 2a and top case 2b are joined by ultrasonic welding.

FIG. 8(a) is a perspective view of the speaker housing 32, FIG. 8(b) is a rear view of the speaker housing 32, FIG. 9(a) is a perspective view of the terminal unit 33, and FIG. 9(a) is a bottom view of the terminal unit 33.

The LED window 34 mounted in a corner of the box 2 has slant surfaces 34a, 34b, as shown in FIG. 10, for distributing light from one LED lamp 20 in directions of side surfaces 2d, 2e of box 2 adjacent the LED window 34.

As shown in FIG. 11, the jack unit 4 has a key insertion hole 41 for receiving a rack K1 of a key K (see FIG. 19), and a set button pin insertion hole 42 for receiving a projecting pin K2 of key K.

As shown in FIG. 13, the key insertion bore 41 has, mounted therein, a pinion gear 43 rotatable by the rack K1 inserted into the key insertion bore 41, and a movement check spring 44 for checking movement of a set button pin 45 mounted in the set button pin insertion bore 42 (see FIG. 12).

The pinion gear 43 is rotatably supported in the main body of jack unit 4, with a part thereof projecting into the key insertion bore 41, and the other part projecting outside the jack unit 4.

FIG. 11(a) is a perspective view of the jack unit 4, and FIG. 11(b) is a side view of the jack unit 4.

The set button pin insertion bore 42 has the set button pin 45 slidably mounted in the set button pin insertion bore 42. A contact spring 46 formed of metal is attached to an end of the set button pin insertion bore 42 to be vertically pivotable when pushed by the set button pin 45.

As shown in FIG. 12, the set button pin 45 includes an operated portion 45a pushed from outside the box 2, a positioning portion 45b for positioning the set button pin 45 in a particular location inside the set button pin insertion bore 42, a spring storing portion 45c storing a coil spring 47 (FIG. 14) for biasing the set button pin 45 in a direction opposite to the inserting direction of the pin K2, and an end 45g for pushing the contact spring 46 to swing the contact spring up and down.

FIG. 12(a) is a plan view of the set button pin 45, and FIG. 12(b) is a sectional view of the set button pin 45.

As shown in FIG. 14, a projection 42a is formed in a space defined by the spring storing portion 45c and inner walls of the set button pin insertion bore 42 to project from the inner walls of the set button pin insertion bore 42 to check movement in the sliding direction of the set button pin 45.

As shown in FIG. 14, the coil spring 47 is disposed between inner walls of the spring storing portion 45c and the projection 42a. Thus, as noted hereinbefore, the set button pin 45 is biased in the direction opposite to the inserting direction of the pin K2.

The positioning portion 45b of set button pin 45 has a positioning bulge 45d having elasticity to be movable in the projecting direction. An inner wall of the set button pin insertion bore 42 includes a recess 42b for engaging the positioning bulge 45d when the set button pin 45 is pushed.

When the set button pin 45 is pushed, the end 45g of set button pin 45 contacts the contact spring 46 to swing the contact spring 46 up and down. With this swinging movement, a free end of contact spring 46 touches the circuit board 30. As a result, the two terminals on the circuit board 30 are short-circuited.

The short circuit of the two terminals causes power to be supplied from battery V each circuit in the box 2. This contact spring 46 corresponds to the power supply switch 6 in FIG. 1.

As shown in FIGS. 13 and 14, the jack unit 4 has the movement check spring 44. The movement check spring 44 is formed of a thin metal piece to be elastically deformable. One end is fixed to one side of the key insertion bore 41 to act as a proximal end, and the other end is a free end 44a pivotable through elastic deformation.

As shown in FIG. 14, when the set button pin 45 is pushed, the free end 44a of the movement check spring 44 is pressed by the elastic action of movement check spring 44, against an engaging portion 45e formed on an outer surface of the spring storing portion 45e of set button pin 45. An intermediate portion 44b between the proximal end and free end 44a of movement check spring 44 extends across the key insertion bore 41.

Top case 2b includes a slider 5 (see FIG. 15) having a rack 5a meshed with the pinion gear 43 of jack unit 4.

As shown in FIG. 5, the slider 5 has a proximal portion 5b thereof slidably engaging a guide portion 2f formed on an inner wall of the top case 2b, which is slidable in two directions indicated by arrows a, b. A forward end of an elastically deformable extension 5c extending from an intermediate portion between rack 5a and proximal portion 5b engages an engaging portion 2g of the top case 2b, so that the elasticity of the extension 5c applies a biasing force in the direction of arrow a.

In the drawings, 2h and 2i denote projections for preventing inclination of slider 5. 2j denotes projections for holding the speaker housing 32 in place. 2k denotes projections for reinforcing contact between terminals 33a, 33b and terminals on the circuit board 30. When the bottom case 2a and top case 2b are joined by ultrasonic welding, the projections 2k press the terminals 33a, 33b to the circuit board.

To start operation of the sensor tag 1, the set button pin 45 is pushed with the projection pin K2 of key K to turn on the power supply switch 6. A mechanism for maintaining the power supply switch 6 in the ON state will be described next.

The set button pin 45 is maintained at first in the position shown in FIG. 16, with the free end of movement check spring 44 engaged with an engaging portion 45f of set button pin 45.

When operated portion 45a of set button pin 45 in the jack unit 4 is pushed into the depth with the projection pin K2 of key K, as shown in FIG. 17, the end 45g of set button pin 45 contacts the contact spring 46, and swings the contact spring 46. With this swinging movement, the free end of contact spring 46 touches the circuit board, and causes a short circuit between the two terminals on the circuit board.

This turns on the power supply switch 6, and starts the power supply from the battery V to each circuit in the main case 101.

When the set button pin 45 is pushed then, the coil spring 47 is compressed to push back the set button pin 45 outside the box 2 (in the direction opposite to the inserting direction of set button pin 45). However, the engaging bulge 45d of set button pin 45 and engaging recess 42d of set button pin insertion bore 42 engage each other, and the free end 44a of movement check spring 44 extending from the key insertion bore 41 engages the engaging portion 45e on the outer surface of spring storing potion 45c. Consequently, that position is maintained against the biasing force of coil spring 47.

A mechanism for turning off the power supply switch 6 to stop the operation of sensor tag 1 will be described next.

In the state shown in FIG. 17, when the rack K1 is inserted into the key insertion bore 41, the rack K1 presses the movement check spring 44 extending across the key insertion bore 41, and rotates the pinion gear 43 meshed with the the rack K1.

When the rock K1 presses the intermediate portion 44b of movement check spring 44, the intermediate portion 44b of movement check spring 44 pushed against a wall of the key insertion born 41. As a result, the free end 44a of movement check spring 44 pivots downward, whereby the free end 44a and the engaging portion 45e of set button pin 45 are disengaged.

When the pinion gear 43 is rotated by the rack K1, as shown in FIG. 18, the rotation of pinion gear 43 causes the slider 5 having the rack 5a engaged with the pinion gear 43 moves in the direction of arrow b.

The slider 5 has a presser portion 5d for contacting the end 45g of set button pin 45 with the sliding movement in the direction of arrow b of slider 5. When the presser portion 5d pushes the end 45g of set button pin 45, the set button pin 45 moves outwardly of the box 2 (in the direction opposite to the direction in which the set button pin 45 is inserted). Consequently, the engaging bulge 45d of set button pin 45 and engaging recess 42b of set button pin insertion bore 42 are disengaged.

As a result, by the return biasing force of coil spring 47 in the spring storing portion 45c, the set button pin 45 returns to the state before the projection pin K2 is inserted (the state of FIG. 16). The contact spring 46 is separated from the two terminals on the circuit board, thereby stopping the power supply from the battery V to each circuit in the box 2.

When the rack K1 is withdrawn from the key insertion bore 42, the slider 5 having slid in the direction of arrow b returns to the original position (the position in FIG. 16) under a biasing force acting in the direction of arrow a due to the elasticity of extension 5c.

FIG. 16, FIG. 17 and FIG. 18(a) are sectional plan views. FIG. 16, FIG. 17 and FIG. 18(b) are sectional side views.

Other embodiments are listed below.

(1) In the above embodiment, the switch 3 is provided on the upper surface 2c of box 2. However, the position of switch 3 is not limited to the upper surface 2c, but may be on a different, side surface. As shown in FIG. 23, for example, switch 3 may be provided on the side surface 2d of box 2.

(2) With the above embodiment, it is impossible to detect a preliminary stealing act to insert a thin plate-like foreign object such as a ruler between sensor tag 1 and object of theft prevention E in order not to allow the operated portion 3a of switch 3 to project from the contact surface. To detect such a preliminary stealing act, the contact surface 2c may have a plurality of projections 2m surrounding the operated portion 3a and extending into the object of theft prevention E.

In this case, the object of theft prevention E should be an object capable of receiving the projections 2m (such as a cardboard box).

(3) In the above embodiment, the operated potion 3a of switch 3 is pivotable in two opposite directions e1, e2, but may be pivotable in other directions as well.

(4) In the above embodiment, and an alarm is outputted by lighting LED lamp 20 and sounding piezoelectric buzzer 21. However, an alarm may be outputted only with piezoelectric buzzer 21. Further, the box 2 may have a transmitting device for transmitting an electric wave, with a device placed in a selected location for receiving the electric wave from the transmitting device and giving an alarm. In this case, an alarm is outputted by transmitting the electric wave from the transmitting device when the sensor tag 1 is detached from the object of theft prevention E.

(5) The alarm outputting device may comprise, instead of piezoelectric buzzer (piezoelectric type buzzer) 21, a different type of buzzer such as the electromagnetic type (but not transmitting an electric wave).

(6) In the above embodiment, openings 10 are formed in the side surface 2n of box 2. However, openings may be formed in a different side surface (such as side surface 2d) as well for releasing the alarm sound.

Then, the openings cannot be blocked up easily, thereby positively preventing a preliminary stealing act to cancel the alarm sound and walk out with the object of theft prevention.

(7) In the above embodiment, the alarm device A receives a signal from the resonance antenna 22, and sounds the piezoelectric buzzer 21 and light LED lamp to give an alarm. However, an electric wave signal my be transmitted upon receipt of the signal from the resonance antenna 22, with a separate device provided to receive the electric wave signal and give an alarm sound or the like.

(8) In the above embodiment, when adjusting the reception sensitivity of resonance antenna 22 by varying the resistance value of resistor R, the adjustment is made by replacing the resistor R with an appropriate one. However, a variable resistor may be used as resistor R, the reception sensitivity of the resonance antenna being adjusted by adjusting the resistance value of the variable resistor.