PURPOSE: To prevent increase in capacity of a power failure compensation system and a power supply due to increased number of sensors by driving a measuring circuit for fire confirmation factors of a sensor only when accessing is made with a polling signal.

CONSTITUTION: A sensor 2 is provided with a basic circuit 2a and a measuring circuit 2b, and the basic circuit 2a and the measuring circuit 2b are connected with each other through a switch contact 2s (which may be replaced by a semiconductor switching element) which is closed or opened by the basic circuit 2a. The basic circuit 2a is provided with both an address setting function for setting the sensor 2 to an arbitrary address and an address identifying function for identifying the address accessed by the polling signal from a fire receiver 1. When the address accessed by the polling signal coincides with the address for which the basic circuit 2a is set, the basic circuit 2a closes the switch contact 2s to supply the measuring circuit 2b with a driving current for measurement.