Smoke Detector

How a Smoke Detector Works
The inner workings of a smoke detector include three main parts: the sensing chamber, a loud horn and a battery (or house voltage power source). A test button lets you know if the battery, sensor and alarm are working properly. Batteries should be replaced yearly, on a regular schedule.

Standard smoke detectors work by ionization; some use a photoelectric cell. With ionization, a tiny amount of radioactive material conducts electricity through the air between two electrodes.

When smoke upsets the current, the alarm sounds. Photoelectric models use a small beam of light. Smoke causes the light to disperse and, when it does, the alarm begins to bleat its warning

Using Smoke Detectors

Most smoke detectors are battery powered but some, particularly those installed during house construction, are wired into a home's electrical system.
Most of the ones that run on line voltage (household current) have a battery backup in case a fire knocks out the house's electrical power.
The main problem with battery-powered smoke detectors is that people don't maintain them. It's estimated that a third of all smoke detectors have missing or dead batteries.
All battery-operated detectors are supposed to signal a low battery; newer models won't close if the battery is removed. New lithium battery models have last up to 10 years; the entire unit is disposable.
Inner workings of a smoke detector include three main parts: the sensing chamber, a loud horn and a battery (or house voltage power source). A test button lets you know if the battery, sensor and alarm are working properly. Batteries should be replaced yearly, on a regular schedule.Smoke detectors should be located on each level of a house and outside each sleeping area (one hallway detector can serve several bedrooms).
Some models sound false alarms when they detect kitchen cooking smoke or high bathroom humidity. It's best not to put them within 20 feet of kitchens, garages, furnaces, hot water heaters, or within 10 feet of a bathroom. Also avoid drafty locations.
A detector should be mounted according to the manufacturer's directions-on the wall or ceiling but not within 4 inches of the corner. The idea is to keep it away from dead air space where smoke might not go.