The principle of ionization type smoke detectors is as shown above. Alpha radiation from the Americium-241 foil increases the ability of air to conduct electricity and thus ionizes the air through Chamber A and B allowing an electrical current flow. In normal operation or when the electrical current flow in Chamber A and B is constant, the electrical potential of S Point is kept balanced. When some particles enter Chambers, alpha radiation is partly absorbed by the smoke particles and consequently the electrical current flow in the Chambers drops , the electrical potential of Point S is unbalanced. This is detected by the detector's electronic circuitry to activate an alarm horn or buzzer.
Detector Technology Limited supply foils in three configurations: