A smoke detector is a device that senses smoke, typically as an indicator of fire. Commercial smoke detectors issue a signal to a fire alarm control panel .
Smoke detectors have audible alarms, visible alarms such as light-emitting diodes (LEDs), or both
They may also have an alarm output to a control unit. Smoke detectors without a built-in alarm come with alarm contacts for output to an external annunciator in the detector base, or to a control unit.