A device that sounds an alarm when it detects smoke or other evidence of fire.

(physics) A device in which the detection of radiation takes place at the depletion junction of a reverse-biased semiconductor junction.

(electronics) A special type of comparator which provides an indication of whether the input voltage is within a specified range.

(Britain) A vehicle equipped with electronic instrumentation that can detect the oscillator of a domestic television, used by the licensing authority to check that a household with no TV licence does not have a television receiver

A device used in security systems that can alert the user of the presence of a moving object.

A timepiece provided with a device for registering and indicating the exact time when a watchman visits certain stations on his beat.

(historical) An apparatus for recording the time when a watchman visits a station on his rounds.

(railways) A bar, connected with a switch, longer than the distance between any two consecutive wheels of a train, laid inside a rail and operated by the wheels so that the switch cannot be thrown until the entire train has passed the switch.

plural of detector bar

(informal) A supposed innate ability to identify sarcasm.