I Didn’t Know That...

Q. Why does my smoke detector have radioactive chemicals in it?

A. Two types of smoke detectors are available. In the simplest, a beam of light is directed at a sensor. If smoke particles pass between the source and sensor, the circuit is broken and an alarm sounds. More sophisticated detectors use a very small amount of a radioactive material that ionizes the air between two electrical plates in the detector, allowing a small electrical current to flow between the plates. Smoke particles entering the chamber increase the resistance of the air, reducing the current and triggering an alarm. These devices are sensitive to much smaller particles than detectors using light beams.