JP4723774B2 - Anti-theft system and anti-theft tag - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an anti-theft system comprising an anti-theft tag that outputs an alarm to prevent theft of an object and a transmitting device that transmits a predetermined signal for the anti-theft tag to output an alarm. about the anti-theft tags to be used.
[0002]
[Prior art]
Conventionally, a store that displays and sells products such as compact discs and software packages often employs an anti-theft system described below in order to prevent the theft of these products.
[0003]
FIG. 10 is a schematic diagram for explaining a conventional antitheft system.
[0004]
In the figure, reference numerals 40 and 40 denote gate panels arranged opposite to the outlets of the store, and the gate panels 40 and 40 always transmit predetermined signals to appropriate areas.
The gate panel 40 includes a signal generation circuit for generating a predetermined signal and an antenna output unit for emitting a signal generated by the signal generation circuit, and a control power source and an antenna for supplying power to the signal generation circuit An output power supply for supplying power to the output unit.
The anti-theft tag 50 includes an antenna input unit that receives signals transmitted from the gate panels 40 and 40, a signal processing unit that determines whether or not the signal received at the antenna input unit is a predetermined signal, and prevents theft. A detection unit for detecting an attachment state with respect to the product T to be processed, a buzzer for outputting an alarm when a predetermined signal is received, or when the product T is inappropriately removed from the product T, and a power source are incorporated.
Since signals emitted from the gate panels 40 and 40 are attenuated in the air, there is a signal reachable distance. In the anti-theft tag 50, if the received signal is smaller than a predetermined value, the anti-theft tag 50 is not regarded as a signal for outputting an alarm. There is a signal reachable distance determined from the combination of the gate panel 40 and the anti-theft tag 50. When someone takes away the product with the anti-theft tag 50 attached and goes out of the exit, and enters the reach range of signals emitted from the gate panels 40, 40, the antenna input portion of the anti-theft tag 50 The signal is received and an alarm is output.
[0005]
FIG. 11 is a perspective view of a conventional antitheft tag.
[0006]
An opening 52 is provided on the surface 51 of the rectangular parallelepiped antitheft tag 50, and the lever 54 of the push switch 53 protrudes from the opening 52 so as to be able to advance and retreat. The lever 54 is urged in a direction to be separated from the surface 51. When a required pressing force is applied to the lever 54, the lever 54 is retracted into the antitheft tag 50 and the push switch 53 is opened. When the pressing force is removed, the push switch 53 projects outward from the opening 52, and the push switch 53 is closed.
When the anti-theft tag 50 is attached to the product T to be protected from theft, the surface 51 from which the lever 54 of the push switch 53 protrudes is brought into contact with the product T, and the anti-theft tag 50 and the product T are transparent made of synthetic resin. The antitheft tag 50 is fixed to the product T by winding it with a sheet member such as a sheet or a translucent sheet.
[0007]
The anti-theft tag 50 includes an antenna input unit for receiving a signal transmitted from the gate panel 40, a detection unit for detecting the open / closed state of the push switch 53, a buzzer for outputting an alarm, and a power source for driving them. is doing.
In the anti-theft tag 50, when a signal transmitted from the gate panel 40 is received or when the detection unit detects that the push switch 53 is closed, the buzzer is activated and an alarm sound is output. That is, when the above-described sheet member is peeled off and the anti-theft tag 50 is removed from the product T, the lever 54 of the push switch 53 is urged to the outside of the anti-theft tag 50 and the push switch 53 is closed. And output an alarm. Further, when the anti-theft tag 50 is fixed and the product T is to be taken from the store, the gate panel 40, 40 is approached and the signal transmitted from the gate panel 40, 40 is within the reachable range. The anti-theft tag 50 receives signals transmitted from the gate panels 40 and 40 and outputs an alarm.
[0008]
However, depending on the floor plan of the store, there may be a case where it is desired to change the reach distance of signals transmitted from the gate panels 40 and 40. For example, when the sales area of a store is small and a product shelf is installed in the immediate vicinity of the gate panels 40 and 40, and the product T must be displayed, the reach distance of signals transmitted from the gate panels 40 and 40 Must be set to be shorter.
Moreover, it is necessary to change the reach distance of the signal transmitted from the gate panels 40 and 40 depending on the frontage of the store. That is, when the frontage is wide, the reach distance of the transmitted signal is increased so that there is no area where the signal from each gate panel 40, 40 does not reach in the middle between the two gate panels 40, 40. Conversely, when the frontage is narrow, it is possible to shorten the reach distance of the transmitted signal.
[0009]
In order to cope with such a problem, the conventional gate panel 40 prepares a control power source to be supplied to the signal generation circuit and an output power source to be supplied to the antenna, and adjusts the output power source to adjust the output power source. The reach of the signal to be sent was adjusted.
In other words, when shortening the signal reach, suppress the output of the output power supply to reduce the size of the signal transmitted from the antenna output unit, and conversely to increase the signal reach, Increasing the output of the power supply for power and increasing the magnitude of the signal transmitted from the antenna output unit has been performed.
[0010]
[Problems to be solved by the invention]
However, in the conventional gate panel, when the control power supply to be supplied to the signal generation circuit and the output power supply to be supplied to the antenna output unit are made common to operate with one power source, the antenna circuit of the antenna output unit (for example, The voltage applied to the LC circuit) cannot be set smaller than the operating voltage of the control circuit such as the signal generation circuit, and thus it is difficult to change the signal reach distance. Therefore, since it is necessary to prepare two power sources, that is, a control power source and an output power source, in order to adjust the reach of the signal to be transmitted, the gate panel is compact and inexpensive, and includes a gate panel and an antitheft tag. Development of an anti-theft system has been desired.
[0011]
The present invention has been made in view of such circumstances, a signal generation circuit that generates a pulse signal, and a transmission device that includes a transmission circuit that transmits a signal corresponding to the input of the generated pulse signal. A plurality of power supplies are provided by including a receiving circuit that receives a signal and an antitheft tag that outputs an alarm based on the received signal, and that can change the pulse width of the generated pulse signal. The anti-theft system that can easily change the reach of the signal sent from the sending device without using the device and can output an alarm when it falls within the reach of the sent signal The purpose is to provide.
[0014]
Still another object of the present invention is that the received signal is analyzed only when the amplitude of the received signal is larger than a predetermined value, and thus the signal is transmitted within the reach of the signal transmitted from the transmitting device. In this case, an anti-theft tag capable of outputting an alarm is provided.
[0015]
Still another object of the present invention is to provide an anti-theft tag capable of identifying a received signal based on the frequency of the signal and outputting an alarm by acquiring information related to the frequency of the received signal. .
[0016]
[Means for Solving the Problems]
The anti-theft system according to the first aspect of the present invention has a signal generation circuit for generating a pulse signal and an input terminal for the pulse signal generated by the signal generation circuit, and transmits a signal corresponding to the input pulse signal. A transmitter having a circuit, a detection circuit for detecting an attachment state to an object to be protected from theft, a receiver circuit for receiving a signal transmitted from the transmitter, and analyzing a signal received by the receiver circuit In the anti-theft system, comprising a signal analysis unit and comprising an anti-theft tag for outputting an alarm based on a detection result by the detection circuit or an analysis result by the signal analysis unit, the signal generation circuit generates a pulse Yes forms the pulse width of the signal can be changed, the signal analysis unit, the amplitude of the received signal only if greater than a predetermined value, in order to analyze Nashitea It is characterized in.
[0019]
The anti-theft system according to the second invention is characterized in that the signal transmitted from the transmission circuit is a signal obtained by modulating a pulse signal input to the transmission circuit.
[0020]
The anti-theft system according to a third aspect of the invention is characterized in that the signal analysis unit is configured to acquire information related to the frequency of the received signal.
[0023]
An anti-theft tag according to a fourth aspect of the present invention is a detection circuit for detecting an attachment state to an object to be prevented from being stolen, a receiving circuit for receiving a signal transmitted from the transmitting device, and a signal received by the receiving circuit. And a signal analysis unit that performs analysis of the anti-theft tag for outputting an alarm based on a detection result by the detection circuit or an analysis result by the signal analysis unit, wherein the signal analysis unit The analysis is performed only when the amplitude is larger than a predetermined value.
[0024]
The anti-theft tag according to a fifth aspect of the invention is characterized in that the signal analysis unit is adapted to acquire information relating to the frequency of the received signal.
[0025]
In the present invention, by adjusting the pulse width of the signal generated by the signal generating circuit, it is possible to adjust the magnitude of the current flowing through the antenna circuit, as a result, the signal transmitted from the antenna circuit The size of can be adjusted. Therefore, without using a plurality of power supply by a child adjusting the pulse signal to be input to the oscillation circuit, reach of the signal transmitted from the transmitter it is possible to easily change the outgoing signal When entering the reachable range, the anti-theft tag can output an alarm.
[0026]
In the present invention, the signal input to the transmission circuit is modulated and then transmitted. Therefore, the signal transmitted from the transmission device can be varied by changing the modulation period.
[0027]
In the present invention, analysis is performed only when the amplitude of the received signal is greater than a predetermined value. Therefore, an alarm can be output when the signal is transmitted from the transmitting device.
[0028]
In the present invention, information related to the frequency of the received signal is acquired. Therefore, it is possible to identify the signal transmitted from the transmission device by the frequency and output an alarm.
[0031]
In the present invention, the received signal is analyzed only when the amplitude of the received signal is larger than the predetermined value, and an alarm is output based on the analysis result. Therefore, the antitheft tag can output an alarm only when it falls within the reach of the signal transmitted from the transmission device.
[0032]
In the present invention, information related to the frequency of the received signal is acquired. Therefore, it is possible to identify the signal transmitted from the transmission device by the frequency and output an alarm.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
FIG. 1 is an explanatory diagram for explaining the anti-theft system of the present invention, and FIG. 2 is a perspective view showing an example of the anti-theft tag of the present invention.
[0034]
As shown in FIG. 2, two insertion holes for inserting the insertion portion of the wire 20 are formed on one end face of the rectangular parallelepiped antitheft tag 2, and both ends of the conductive wire 20 are inserted into both insertion holes. The part is detachably fitted. When such an anti-theft tag 2 is attached to a product T such as clothes, one end of the wire 20 is fitted into one insertion hole of the anti-theft tag 2, and the other end of the wire 20 is a button of a jacket or shirt. A product tag such as a product tag provided at a hole or a collar of clothing is inserted through the attachment site of the product T, and the other end of the wire 20 is inserted into the other insertion hole of the antitheft tag 2.
[0035]
Gate panels 1 and 1 for transmitting a predetermined signal are arranged opposite to each other in the vicinity of the store entrance. The gate panels 1 and 1 are configured to transmit predetermined signals to appropriate areas. The anti-theft tag 2 includes an antenna input unit 21 for receiving a signal transmitted from the gate panels 1 and 1, a buzzer 27, etc. (see FIG. 3). The antitheft tag 2 prevents the theft of the product T by outputting an alarm when a predetermined signal is received from the gate panels 1 and 1.
[0036]
Further, the wire 20 described above functions as a normally closed contact, and when the wire 20 is pulled out from the insertion hole of the antitheft tag 2 or the wire 20 is cut in order to remove the antitheft tag 2 from the product T. The detection unit 24 (see FIG. 3) of the antitheft tag 2 detects it and outputs an alarm.
[0037]
FIG. 3 is a block diagram of the anti-theft system of the present invention.
In the figure, reference numeral 1 denotes a gate panel that is installed in the vicinity of a store entrance and transmits a predetermined signal to the anti-theft tag 2.
The gate panel 1 includes a signal generation circuit 11 that generates a pulse signal having a predetermined period (for example, 22 kHz), and an antenna output unit 12 that transmits a signal corresponding to the signal input from the signal generation circuit 11.
The signal generation circuit 11 generates a pulse signal having a predetermined period, generates a burst control signal, and generates a code signal as described later based on the pulse signal and the burst control signal. The H level portion of the code signal is composed of a pulse signal having a predetermined period, and the signal generation circuit 11 adjusts the pulse width of the pulse signal, thereby adjusting the amplitude of the signal output from the antenna output unit 12.
[0038]
The anti-theft tag 2 receives a signal output from the antenna output unit 12 of the gate panel 1, converts it into a code signal and outputs it, and a code for identifying a code signal given from the antenna input unit 21 An identification unit 22 is provided. The signal processing unit 25 gives an alarm signal to the drive unit 26 based on the signal input from the code identification unit 22 to drive the buzzer 27 and the LED 28.
Further, the anti-theft tag 2 includes a detection unit 24. The detection part 24 detects the attachment state of the anti-theft tag 2 to the goods T which should prevent the theft as mentioned above. When the anti-theft tag 2 is normally attached to the product T, the wire 20 of the anti-theft tag 2 functions as a normally closed contact, and no alarm is output. On the other hand, when the wire 20 is pulled out from the insertion hole of the anti-theft tag 2 and the anti-theft tag 2 is improperly removed from the product T, or when the wire 20 is cut and improperly removed from the product T, it is detected. The unit 24 detects that the wire 20 is not conductive, and gives a predetermined signal to the input unit 23. The signal processing unit 25 gives an alarm signal to the driving unit 26 based on the signal given from the input unit 23 to drive the buzzer 27 and the LED 28.
[0039]
Further, when it is necessary to remove the anti-theft tag 2 from the product T without outputting an alarm for reasons such as replacement work of the product T, for example, a transmitter (not shown) that transmits a specific signal such as a reset signal. ) Is used to give a reset signal to the antenna input unit 21 of the anti-theft tag 2.
In this case, the signal processing unit 25 gives an alarm signal to the drive unit 26 even when the detection unit 24 detects that the wire 20 is not conductive and normally outputs an alarm. There is no alarm output.
[0040]
FIG. 4 is a block diagram showing details of the antenna output unit 12.
The antenna output unit 12 includes a bridge circuit, and when the signal from the signal generation circuit 11 is input to the four input terminals t1, t2, t3, and t4, the output voltage corresponding to the input signal is changed to the coil L. A signal is transmitted.
An output power supply Vo is connected between the input terminals t1 and t3, and the input terminals t2 and t4 are grounded. One terminal of the coil L is connected between the input terminals t1 and t2, and the other terminal of the coil L is connected between the input terminals t3 and t4.
The connection line from the signal generation circuit 11 is connected so that the same signal is input to the input terminals t1 and t4, and is connected so that the same signal is input to the input terminals t2 and t3. Yes.
[0041]
FIG. 5 is a waveform diagram illustrating an example of a signal input to the antenna output unit 12.
As shown in FIG. 5A, the signal S1 is a signal input to the input terminals t1 and t4 (or the input terminals t2 and t3), and is composed of a square wave having a period f (for example, 22 kHz). . Similarly, the signal S2 is formed of a square wave having a period f and a phase opposite to that of the signal S1, and is input to the input terminals t2 and t3 (or the input terminals t1 and t4).
When the signals S1 and S2 are input to the input terminals t1, t2, t3, and t4, the voltage applied to the coil L is a pulse voltage having the maximum voltage V _in and the period f (FIG. 5C). In this case, the current flowing through the coil L has a substantially sine waveform having an amplitude I _in and a period f.
Therefore, the signal transmitted from the antenna output unit 12 is a signal having an amplitude proportional to the amplitude I _in.
[0042]
On the other hand, when the signals S1 ′ and S2 ′ (FIGS. 5 (e) and (f)) with narrow pulse widths are input to the antenna output unit 12 without changing the period f, the voltage applied to the coil L is In addition, the maximum voltage V _in ′ does not change and only the pulse width decreases. In this case, the amplitude I _in ′ of the current flowing through the coil L is reduced, and as a result, the amplitude of the signal transmitted from the antenna output unit 12 is also reduced.
Thus, in the gate panel 1 of the present invention, the magnitude of the signal transmitted from the antenna output unit 12 can be adjusted by adjusting the signal input to the antenna output unit 12.
[0043]
FIG. 6 is a graph showing the relationship between the pulse width input to the antenna output unit 12 and the signal arrival distance.
The horizontal axis represents the pulse width (duty [%]) input to the antenna output unit 12, and the vertical axis represents the signal arrival distance. Here, the signal reachable distance is the same as the gate panel 1 when the alarm is output for the first time when the antitheft tag 2 is brought closer to the point away from the gate panel 1 while the signal is transmitted from the gate panel 1. This is the distance between the antitheft tag 2.
From the result of FIG. 6, it can be seen that the signal arrival distance varies in proportion to the pulse width of the signal input to the antenna output unit 12. If you want to increase the signal reach, you can lengthen it by widening the pulse width. Conversely, if you want to shorten the signal reach, you can shorten it by narrowing the pulse width. is there. According to the observation results of the inventors, when the duty is 14.7%, the signal reach distance is about 180 cm, and when the duty is 21.9%, the signal reach distance is 240 cm.
As described above, in the present invention, the signal arrival distance can be easily changed by changing the pulse width of the pulse signal input to the antenna output unit 12.
[0044]
Further, the signal generation circuit 11 generates a code signal as described later using the signals S1 and S2 having a predetermined period and the burst control signal.
7 and 8 are explanatory diagrams for explaining a configuration example of a code signal transmitted from the gate panel 1. FIG.
The code signal is composed of a frame having a length of 140 msec consisting of a start bit and a data bit, and the code signal and an L level frame having a length of 50 msec are alternately transmitted from the gate panel 1 at all times.
The start bit at the head of the code signal has a length of 20 msec, 15 msec from the rising edge is H level, and the remaining 5 msec is L level. The data bit is composed of a combination of data bit “0” and data bit “1”. The data bit “0” has a length of 8 msec, 2 msec from the rising edge is H level, and the remaining 6 msec is L level. The data bit “1” has a length of 12 msec, 8 msec from the rising edge is H level, and the remaining 4 msec is L level.
[0045]
This code signal is composed of a start bit S0 followed by data bits D0 to D11. Of the data bits D0 to D11, the data bits D0 to D5 are data codes, which are interleaved and transmitted in the order of D2D3D4D5D0D1.
As shown in FIG. 7, the data bits D6 to D11 are obtained by inverting the bits of the data codes D0 to D5. Further, the data bits D6 to D11 are further inverted on the receiving side, and the data codes D0 to D5 and the data codes D6 to D11 are obtained. This is for confirming that the signal has been correctly received when.
For example, when the data codes D0 to D5 are “010101”, the code signal is “S0 010110101010”.
[0046]
FIG. 9 is a flowchart showing a procedure for processing a signal received by the anti-theft tag 2.
[0047]
The antenna input unit 21 demodulates by generating an H level LFIN signal only while receiving a signal from the gate panel 1 installed at the entrance / exit of the area where the antitheft tag 2 is installed.
First, the antenna input unit 21 determines whether any signal is received (step S1). When the signal is not received (S1: NO), it waits until the signal is received.
When a signal is received (S1: YES), it is determined whether the amplitude of the received signal is greater than a predetermined value (step S2). If the magnitude of the received signal is smaller than the predetermined value (S2: NO), the process returns to S1.
[0048]
Next, the antenna input unit 21 determines whether or not the H level portion (LFIN (H)) of the LFIN signal is longer than 12 msec by detecting the level, for example, every 5 seconds from the rise of the signal (step S3). ) If it is not long (S3: NO), it is ignored as a meaningless signal. If it is long (S3: YES), the LFIN signal is set as the start bit S0, and reading of data bits is started (step S4).
[0049]
The antenna input unit 21 compares the lengths of the demodulated LFIN signals, for example, by detecting the level every 5 seconds from the rising edge.
The antenna input unit 21 compares whether or not the length of LFIN (H) of the read data bits is longer than 20 msec (step S5). If the length is long (S5: YES), the following read is performed as a meaningless signal. Cancel. Further, it is determined whether or not the length of the L-level LFIN signal (LFIN (L)) of the read data bit is longer than 20 msec (step S6). If the length is long (S6: YES), as a meaningless signal, Stop reading the following.
Further, when the antenna input unit 21 confirms a new start bit S0 during reading of data bits, the antenna input unit 21 discards the already read data bits and starts reading new data bits.
[0050]
When 12 bits of data bits are read, the antenna input unit 21 completes reading of the data bits (step S7). Next, the antenna input unit 21 determines whether or not the read data bits D0 to D5 match the inverted signals of D6 to D11 (step S8). If they do not match (S8: NO), the antenna input unit 21 accurately The received data bits are discarded as if they could not be received. If they match (S8: YES), the sequence of LFIN signals of the read data bits is given to the code identification unit 22 as a code.
The code identifying unit 22 identifies the given code (step S9), and determines whether the code is a predetermined code (step S10). If it is not a predetermined code (S10: NO), it is determined that the code signal is of a different type, and the process returns to S1.
When it is determined that the signal is a predetermined code signal (S10: YES), an alarm signal is given to the signal processing unit 25, thereby driving the driving unit 26 and driving the buzzer 27 and the LED 28 to output an alarm (step S11). ).
[0051]
Although the anti-theft tag 2 in which the anti-theft tag 2 is attached to the product T by the wire 20 has been described in the present embodiment, the present invention is not limited to this and is pushed to one surface of a rectangular parallelepiped casing. A switch lever is provided so as to be able to advance and retreat, the lever of the push switch is brought into contact with the product T, the lever is retracted into the housing, and the housing and the product are wound by a synthetic resin sheet member. The present invention can also be applied to an anti-theft device in which a casing is fixed to an object. The lever of the push switch is energized in a direction away from the casing, and when the casing is removed from the object, the lever protrudes to output an alarm.
[0052]
It should be noted that the reference numerals are used in the claims to make the comparison with the drawings convenient, but the present invention is not limited to the structure of the attached drawings by this entry.
[0053]
【The invention's effect】
As described above in detail, according to the invention, by adjusting the pulse width of the signal generated by the signal generating circuit, it is possible to adjust the magnitude of the current flowing through the antenna circuit, as a result, The magnitude of the signal transmitted by the antenna circuit can be adjusted. Therefore, without using a plurality of power supply by a child adjusting the pulse signal to be input to the oscillation circuit, reach of the signal transmitted from the transmitter it is possible to easily change the outgoing signal When entering the reachable range, the anti-theft tag can output an alarm.
[0054]
In the case of the present invention, the signal input to the transmission circuit is modulated and then transmitted. Therefore, the signal transmitted from the transmission device can be varied by changing the modulation period.
[0055]
In the case of the present invention, the analysis is performed only when the amplitude of the received signal is larger than a predetermined value. Therefore, an alarm can be output when the signal is transmitted from the transmitting device.
[0056]
In the case of the present invention, information related to the frequency of the received signal is acquired. Therefore, it is possible to identify the signal transmitted from the transmission device by the frequency and output an alarm.
[0059]
According to the present invention, the received signal is analyzed only when the amplitude of the received signal is larger than a predetermined value, and an alarm is output based on the analysis result. Therefore, the antitheft tag can output an alarm only when it falls within the reach of the signal transmitted from the transmission device.
[0060]
In the case of the present invention, information related to the frequency of the received signal is acquired. Therefore, the present invention has an excellent effect that a signal transmitted from the transmitting device can be identified by frequency and an alarm can be output.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram for explaining a theft prevention system of the present invention.
FIG. 2 is a perspective view showing an example of an antitheft tag according to the present invention.
FIG. 3 is a block diagram of the anti-theft system of the present invention.
FIG. 4 is a block diagram showing details of an antenna output unit.
FIG. 5 is a waveform diagram showing an example of a signal input to an antenna output unit.
FIG. 6 is a graph showing a relationship between a pulse width input to an antenna output unit and a signal reach distance.
FIG. 7 is an explanatory diagram illustrating a configuration example of a code signal transmitted by a gate panel.
FIG. 8 is an explanatory diagram illustrating a configuration example of a code signal transmitted from a gate panel.
FIG. 9 is a flowchart showing a procedure for processing a signal received by an anti-theft tag.
FIG. 10 is a schematic diagram illustrating a conventional antitheft system.
FIG. 11 is a perspective view of a conventional antitheft tag.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Gate panel 11 Signal generation circuit 12 Antenna output part 2 Anti-theft tag 20 Wire 21 Antenna input part 22 Code identification part 23 Input part 24 Detection part 25 Signal processing part 26 Drive part 27 Buzzer 28 LED

Claims (5)

A signal generation circuit (11) for generating a pulse signal, and input terminals (t1, t2, t3, t4) for the pulse signal generated by the signal generation circuit (11), and corresponding to the input pulse signal A transmission device (1) having a transmission circuit (12) for transmitting a signal, a detection circuit (24) for detecting an attachment state to an object to be protected from theft, and a signal transmitted from the transmission device (1) A reception circuit (21) for receiving, and a signal analysis unit (22) for analyzing a signal received by the reception circuit (21), and a detection result by the detection circuit (24) or a signal analysis unit (22) In the anti-theft system (1, 2) comprising the anti-theft tag (2) that is supposed to output an alarm based on the analysis result,
The signal generation circuit (11) can change the pulse width of the pulse signal to be generated, and the signal analysis unit (22) should analyze only when the amplitude of the received signal is larger than a predetermined value. An anti-theft system (1, 2) characterized by being. The signal transmitted from the transmitter circuit (12), anti-theft system according to claim 1, wherein a signal obtained by modulating a pulse signal input to the oscillator circuit (12) (1,2) . The anti-theft system (1, 2) according to claim 1 or 2 , wherein the signal analysis unit (22) is adapted to acquire information relating to a frequency of the received signal. A detection circuit (24) for detecting an attachment state to an object to be protected from theft, a reception circuit (21) for receiving a signal transmitted from the transmission device (1), and reception by the reception circuit (21) A signal analysis unit (22) for analyzing the received signal, and an anti-theft tag for outputting an alarm based on the detection result by the detection circuit (24) or the analysis result by the signal analysis unit (22) 2)
The anti-theft tag (2), wherein the signal analysis unit (22) should analyze only when the amplitude of the received signal is larger than a predetermined value. The anti-theft tag (2) according to claim 4 , wherein the signal analysis unit (22) is adapted to acquire information relating to the frequency of the received signal.

Images