Are you looking for two wire smoke detectors ？

For smoke detectors, there are many types, such as wired (divided into 2 lines/3 lines/4 lines)/independent/networked/wireless/wifi models, etc. Here we will introduce you to two wire smoke detector.

The two wire smoke detector will be used together with the fire control panel. two wire smoke detectors use the same wire pair to provide both power to the detector as well as carrying the signal back in case smoke is detected. The wires connect to the PGM terminals on your alarm system( fire control panel).. The above is the working principle of the two wire smoke detector.

The two wire smoke detector introduced here is a photoelectric smoke detector, which uses the principle that particles in smoke refract infrared light to detect fire. In the smokeless state, the receiving tube only receives weak infrared light. When smoke enters, the light signal received is enhanced due to the emission effect. When the smoke reaches a certain concentration, the detector outputs an alarm signal. Used for indoor smoke monitoring in residences, shopping malls, hotels, apartments, offices, schools, etc.

Having said so much, it might as well take a look at how the two wire smoke detector triggers the alarm, please see the following video. 

If you are looking for a two wire smoke detector, please click "two wire smoke detector" to a detailed understanding.