How do Smoke Alarms Work?

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  • Written By: J. Beam
  • Edited By: Bronwyn Harris
  • Last Modified Date: 09 October 2019
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The majority of smoke alarms have one of two types of detectors built in. The photoelectric detector employs light technology and sensors. Inside an alarm with a photoelectric detector, there are beams of light that radiate at a ninety-degree angle from a built-in sensor. In the event of smoke, the smoke particles interrupt the light beams causing them to reflect off of minute particles and trigger the sensor. This is when the alarm sounds.

The other most common type of smoke alarms have ionization detectors that work off of an electrical current created by electrons and ions moving between two internal plates. When smoke enters the interior, the current is disrupted and an alarm sounds. Alarms with ionization detectors are the most common type found in homes. Though they contain miniscule amounts of radiation, they are perfectly safe for use in the home. Still, the internal mechanisms of this type of smoke alarm should not be handled directly.

Every home should have working smoke alarms installed on each floor of the home. Proper maintenance is necessary to ensure they are in working order year round, but it is as simple as replacing the batteries twice each year and testing the alarm function by pressing the test button once each month. Most smoke alarms work off of 9-volt batteries.


When selecting a new smoke alarm, check that the alarm sound emitted is at a pitch and noise level that will wake you from a sound sleep. There are some types of smoke alarms that have programmable alarms that allow you to record your own voice as well. Determine which type of alarm would get your attention quickest and then perform the necessary routine maintenance. Hopefully your smoke alarm will never need to save your life, but knowing you have a properly working one that could will help you sleep a little better at night.


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Post 5

a smoke alarm is designed to detect smoke which will cause the siren to sound. this is to give you time to get out of the danger zone.

the reason hardwired alarms have a battery is purely as a back-up. when you have a power cut the smoke alarm can still operate

Post 3

what is a smoke alarm used for?

Post 2

To Anon32112: My best educated guess as to why a smoke alarm that's wired into the mains still requires a battery is that in case of a power cut the alarm is still functional. A mains only powered alarm would be useless otherwise if there is a power cut.

Post 1

I replaced the battery in a smoke alarm that is also wired to the ceiling. Why does the alarm have both an electrical and a battery source? Thanks

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