Security system

1. A security system for monitoring theft of a merchandise item placed on a merchandise rack at a shop, the security system comprising:

a sensor attached to the merchandise item;

a slave unit attached to the merchandise rack and connected to one or a plurality of said sensors via a wire; and

a master unit that monitors theft of the merchandise item by wirelessly receiving a signal using a first frequency band from one or a plurality of said slave units,

said slave unit comprising:

detection unit configured to detect one of detachment of said sensor from the merchandise item, detachment of said slave unit from the merchandise rack, and detachment of the wire from said slave unit so as to detect the theft of the merchandise item;

slave-unit-side transmission unit that wirelessly transmits a signal using the first frequency band, configured to transmit, to said master unit, an alarm signal that instructs to start an alarm operation when said detection unit has detected the theft of the merchandise item; and

slave-unit-side receiving unit that wirelessly receives a signal using a second frequency band representing a band different from the first frequency band, configured to receive an instruction from a remote controller that wirelessly transmits various kinds of signals using the second frequency band, and

said master unit comprising:

first master-unit-side receiving unit that wirelessly receives the signal using the first frequency band, configured to receive the alarm signal transmitted by said slave-unit-side transmission unit;

second master-unit-side receiving unit that wirelessly receives the signal using the second frequency band, configured to receive the instruction from the remote controller; and

master-unit-side alarm unit configured to start the alarm operation when said first master-unit-side receiving unit has received the alarm signal.

2. The security system according to claim 1 , wherein

said slave unit further comprises a slave-unit-side memory configured to hold a slave unit ID to be used to identify said slave unit,

said slave-unit-side transmission unit transmits the alarm signal including the slave unit ID held in said slave-unit-side memory,

said master unit further comprises:

a master-unit-side memory configured to hold a slave unit ID of a slave unit as a monitoring target; and

determination unit configured to determine whether the slave unit ID included in the alarm signal received by said first master-unit-side receiving unit matches the slave unit ID held in said master-unit-side memory, and

said master-unit-side alarm unit starts the alarm operation when said determination unit has determined that the slave unit IDs match.

3. The security system according to claim 2 , wherein

said slave unit further comprises slave unit ID generation unit configured to generate the slave unit ID and store the slave unit ID in said slave-unit-side memory,

said slave-unit-side transmission unit transmits a slave unit ID registration signal including the generated slave unit ID, and

said master unit transits to a setting mode when a user operates a predetermined button provided on said master unit, and when said first master-unit-side receiving unit has received the slave unit ID registration signal after the transit to the setting mode, registers the slave unit ID included in the slave unit ID registration signal in said master-unit-side memory as the slave unit ID of the slave unit as the monitoring target.

4. The security system according to claim 1 , wherein

said slave unit further comprises slave-unit-side alarm unit configured to start the alarm operation when said detection unit has detected the theft of the merchandise item,

when said slave-unit-side receiving unit has received, from the remote controller, a reset signal that instructs to stop the alarm operation, said slave-unit-side transmission unit transmits an alarm stop signal that instructs to stop the alarm operation in said master unit,

said slave-unit-side alarm unit stops the alarm operation when said slave-unit-side receiving unit has received the reset signal from the remote controller, and

said master-unit-side alarm unit stops the alarm operation when said first master-unit-side receiving unit has received the alarm stop signal.

5. The security system according to claim 4 , wherein the alarm operation by said master-unit-side alarm unit and said slave-unit-side alarm unit is performed by at least one of generating an audible alarm and turning on an alarm LED.

6. The security system according to claim 1 , wherein

said master unit further comprises master-unit-side transmission unit that wirelessly transmits a signal using the second frequency band, configured to transmit a signal concerning a setting operation for said slave unit, and

said slave unit causes said slave-unit-side receiving unit to receive the signal concerning the setting operation transmitted by said master-unit-side transmission unit.

7. The security system according to claim 1 , wherein the signal using the first frequency band is a high-frequency signal, and the signal using the second frequency band is a low-frequency signal having a frequency lower than that of the signal using the first frequency band.

8. The security system according to claim 1 , the security system further comprising a holder placed on the merchandise rack to detachably hold the merchandise item,

wherein said slave unit is mounted inside said holder.