What do photoelectric smoke detectors and alarms use to operate?

Photoelectric smoke detectors and alarms operate using a beam of light. These devices contain a light source and a light sensor. When smoke enters the detection chamber, it scatters the light emitted by the source. The scattered light then reaches the sensor, triggering the alarm. This method is particularly effective for detecting smoldering fires that produce a lot of smoke but not as much heat, making them an essential safety tool in many environments.

The other options are not used in photoelectric smoke detectors. Thermal sensors rely on detecting temperature changes associated with heat, which is a different technology altogether. Radio waves are not applicable in this context since they are typically associated with communication devices, not smoke detection. Chemical reactions are also not involved, as this is a separate category of detection that relies on changes in the chemical composition of materials rather than physical changes in light scattering. The operation of photoelectric detectors is fundamentally based on the interaction of light and smoke, making the use of a beam of light the correct choice.