noun
A device that detects smoke and raises an alarm; used in fire safety contexts.
煙感知器が火事を知らせてくれた。
The smoke detector alerted us to the fire.
火災報知器 is a broader term for fire alarm devices, while 煙感知器 specifically detects smoke.
Compound of 煙 (smoke) + 感知器 (detector/sensor).