SECURITY SYSTEM

A security system includes a sensor attached to a merchandise item, a slave unit attached to a merchandise rack and connected to one or a plurality of 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 slave units. The slave unit includes a detection means for detecting detachment of the sensor from the merchandise item, or the like so as to detect the theft of the merchandise item, a slave-unit-side transmission means, configured to wirelessly transmit a signal using the first frequency band, for transmitting an alarm signal to the master unit when the theft of the merchandise item has been detected, and a slave-unit-side receiving means, configured to wirelessly receive a signal using a second frequency band representing a band different from the first frequency band, for receiving an instruction from a remote controller that wirelessly transmits various kinds of signals using the second frequency band. The master unit includes a first master-unit-side receiving means, configured to wirelessly receive the signal using the first frequency band, for receiving the alarm signal, a second master-unit-side receiving means, configured to wirelessly receive the signal using the second frequency band, for receiving the instruction from the remote controller, and a master-unit-side alarm means for starting the alarm operation upon receiving the alarm signal.