Since a sensor signal intermitted on the basis of a sensor signal including an abnormality detection signal, detected as a result of a persistence of an abnormal condition of a security sensor, is generated and an intermitted output signal in dependence on an intermitted sensor signal input is transmitted from a wireless transmitter 17 to a receiver 18, a condition in which the intermitted output signal can be transmitted from the wireless transmitter 17 to the receiver 18 can be retained even though the wireless transmitter 17 is of a type capable of transmitting an output signal in the form of, for example, one pulse on the basis of the signal input, and it is therefore possible for the side of the receiver 18 to recognize assuredly the persistence of the abnormal condition.