Technology
How does a smoke detector work?
A smoke detector works by sensing smoke particles in the air and sounding an alarm. The common 'ionization' type uses a tiny amount of radioactive material to detect smoke, while 'photoelectric' types watch for smoke scattering a beam of light.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how a smoke detector works.
Step by step
- 1Ionization detectors pass a small current through ionized air; smoke disrupts it.
- 2That type uses a tiny, safely sealed radioactive source.
- 3Photoelectric detectors shine a light beam that smoke scatters onto a sensor.
- 4Either change triggers a loud alarm.
- 5Photoelectric ones react faster to smoldering fires; ionization to flaming ones.
Frequently asked questions
- How does a smoke detector sense smoke?
- It either detects smoke disrupting a tiny electric current in ionized air, or smoke scattering a light beam onto a sensor — both trigger the alarm.
- Is the radiation in a smoke detector dangerous?
- No. It uses a tiny, sealed amount that can't reach you in normal use; it's safe in the home.
- Which type of smoke detector is better?
- Photoelectric detectors catch slow, smoldering fires faster, while ionization ones react to fast flames — many experts suggest having both.