I have seen 2 wire detectors and horn strobes, and 4 wire detectors and horn strobes. What is the difference? The 2 wires are cheaper.
In 2-wire systems the power and the detector signal are multiplexed onto 2 wires. The detector has to have circuitry to extract the power and multiplex the signal onto the wires, making them slightly more complex. In 4-wire systems the power is separate from the signal, unless there is more than one signal from the detector (i.e. smoke heat). It could be 2 wires for power and 2 wires for a single signal (i.e. smoke), or 1 wire for power, 1 wire for smoke, and 1 wire for heat, with the 4th wire being common to all 3. .
2 Wire Vs 4 Wire Smoke Detector
