Ionisation Smoke Detector
Air in the dual sensing chambers is irradiated to produce ions that travel to the positive and negative electrodes, creating a current flow. As smoke enters the outer chamber, the flow drops and the voltage increases. The detector will then enter the alarm state and the indicator LED lights up.

Optical Smoke Detector
The optical smoke detector uses an internal pulsing LED and a photo-diode at an obtuse angle. In the event of smoke entering the chamber, the light pulse from the LED will be scattered and registered by the photo-diode. The detector will then enter the alarm state and the indicator LED lights up.
 

Heat Detector
The heat detector operates by using a matched pair of thermistors to sense heat. One thermistor is exposed to the ambient temperature, the other is sealed. In normal conditions, the two thermistors register similar temperatures, but, on the development of a fire, the temperature recorded by the exposed thermistor will increase rapidly, resulting in an imbalance of the thermistors and causing the detector to change to the alarm state.

Bases
The bases have been designed to enable detectors to be plugged in without any need for force and have a "one way only" fit.