In a fire alert system energy is harvested from a wire line pair (408) used to provide primary electrical power from a fire panel central monitoring station to a plurality of remote devices (406). The fire panel central monitoring station begins communications with a remote device by modulating the voltage on the wire line pair so as to communicate a first message (502) to one of the plurality of remote devices. Thereafter, one of the remote devices will respond to the first message with a second message (504) by modulating the voltage on the line pair. Energy is selectively harvested from the wire line pair at one or more of the remote devices in accordance with the remote device address specified in the first message.