noun
fire sensor; fire alarm
A device that detects fire or smoke and triggers an alarm. Often used in building safety contexts.
この建物には火災感知器が設置されています。
This building is equipped with fire sensors.
火災報知器 specifically refers to a fire alarm device that actively alerts people, while 火災感知器 emphasizes the detection/sensing function.
Compound of 火災 (fire disaster) + 感知 (detection) + 器 (device).