Learn in the textbookDetection Devices (Distance and Environmental-Quantity Sensors)
DefinitionA smoke sensor (煙センサー) detects smoke particles in the air so that a fire can be reported early.
ExplanationThe photoelectric type (光電式), for example, shines light inside and detects smoke when particles that drift in scatter that light onto a receiver. It is built into home smoke alarms and building fire-safety equipment, and sounds an alarm once the smoke passes a certain density.
AnalogyOn a foggy night you can see the beams of car headlights because tiny droplets scatter the light. The sensor recreates that effect inside a small box to notice smoke.
Memory hookPut the saying "where there's smoke, there's fire" to work: the sensor is a lookout that suspects fire as soon as it sees smoke.