US Patent 8970387 Smoke detector

An alarm for detecting smoke comprises a housing (1) having vents (9) for allowing ingress of smoke into the housing. A sensor chamber (22,26) is disposed within the housing and has vents (24a,24b) for allowing ingress of smoke into the sensor chamber and comprises two parts. A diode emitter and diode sensor (25) is mounted within the sensor chamber for sensing light reflected off smoke. An alarm circuit (32), including detection means for detecting smoke sensed by the sensor diode (25), is supported on a printed circuit board (PCB) (29). The PCB is sandwiched between two halves (22 and 26) of the sensor chamber such that an edge (30) thereof extends part-way into said sensor chamber. The sensor is mounted on, near or adjacent to the edge.