Why does a smoke detector emit a low intermittent beep?

Updated November 21, 2016

Fires kill thousands every year in their homes, especially at night when people are asleep. Such tragedies can be averted, however, because smoke detectors can and do save lives when used properly. Although smoke alarms are crucial home fixtures, homeowners and renters sometimes disable them because they may seem like a nuisance when no fire danger is present. Constant beeping can be a problem, but there are reasons for the noise and ways to make it stop.

How They Work

Smoke detectors are available with three types of sensors: ionisation, photoelectric, and combination sensors. Ionisation smoke alarms have a small electric current inside that, when interrupted by smoke particles, emits a loud warning sound. Photoelectric detectors have a light source and receptor instead of an electric current. When particles get in the way, the light receptor triggers the alarm. Combination smoke alarms have both types of devices.


In addition to the types of sensors they contain, smoke alarms may be powered one of three ways: battery-only, hard-wired, or both. Battery-operated detectors only work when the battery is functional. Hard-wired alarms only work when the electricity is on and the wiring is operating properly. Finally, some hard-wired detectors have a battery backup in case of a power failure.


Properly working smoke detectors make a loud, shrill sound when smoke or other small particles cause it to trigger.

A low, intermittent beep can occur for a few reasons. If your detector has a battery, even if it is also hard-wired, it's likely that the battery is getting weak. Begin by replacing the battery, then be sure to reset the alarm.

If there is no battery at all, the power supply may have suffered an interruption. Again, try resetting the detector. When this doesn't work, the wiring may be defective.

With either a battery-operated or hard-wired smoke alarm, your smoke detector may be malfunctioning due to its age or other mechanical issue. Some alarms are designed to alert you if there's an overall problem with the detector. Before you hire an electrician, try replacing the alarm with a brand new one.

Fire Safety

Smoke detectors are essential to your home. Be sure to place one on each level, with at least one outside of every sleeping area. Placing one inside each bedroom is ideal. You should also create a fire escape plan for your household and do a practice drill so that everyone is familiar with the steps they should take in an emergency.


Never remove the batteries from a detector, even if it's a nuisance, because you might forget to replace them.

Don't put the smoke detector near the stove or vents. In addition to smoke, dust and food particles can trigger the alarm.

Test your smoke detector monthly, but also realise that smoke detectors should be replaced every 10 years.

Consider having your smoke detectors interconnected so that when one sounds, they all do.

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