alarm; warning device
Refers to a device that gives an alarm or warning, such as a fire alarm or security alarm. Often used in compound terms like 火災報知機 (fire alarm).
The fire alarm went off, so we evacuated immediately.
This building is equipped with the latest alarm devices.
アラーム is a common loanword for 'alarm', often used for everyday alarms like alarm clocks. 報知機 is more technical and refers to warning devices.
fire alarm
Compound of 報知 (hōchi, 'notification, information') + 機 (ki, 'machine, device'). The exact historical derivation is uncertain, but the word follows a standard pattern for naming warning devices.