Detection principle
Optical alarms respond to smoke entering a sensing chamber
Common domestic optical alarms use a light source and sensor arranged so smoke particles change the light reaching the sensor. Other approved technologies exist, and different fire types can develop differently.
Heat alarms respond to temperature rather than smoke and are commonly considered for kitchens where normal cooking fumes can make a smoke alarm unsuitable. A heat alarm should not replace smoke detection elsewhere without a suitable design.
Power and warning
The sensor, electronics and sounder all need reliable power
Battery alarms may use replaceable or sealed long-life batteries. Mains alarms normally include standby power and should be installed by a competent electrician where electrical work is required.
Interlinked alarms cause connected devices to sound when one detects a fire. This can improve warning across storeys, closed doors or larger layouts. Specialist visual and vibrating alerts are available for people who may not hear an audible alarm.
Routine assurance
The test control checks the alarm’s electronic warning path
GOV.UK home guidance recommends testing smoke alarms at least monthly. Use the product’s test button or approved remote method and confirm linked devices operate where applicable.
Testing cannot recreate every fire condition or prove indefinite sensor life. Keep the alarm clean as instructed and replace it at the manufacturer’s end-of-life date or when it remains faulty.
- Correct alarm type for the room
- Test produces the expected warning
- Linked alarms operate together where designed
- No paint, cover, dirt or obstruction affects the unit
- Manufacture or replacement date remains legible
Limits
An alarm only protects people who can receive and act on the warning
Closed doors, background noise, hearing loss, sleep, alcohol, medication and distance can affect whether occupants respond. The layout may need linked alarms or specialist warning devices.
Plan escape, keep routes usable and call 999 once safe. Never re-enter because an alarm has stopped.