What battery does a smoke detector take?
Most standalone smoke detectors use a 9V battery. Some models, especially newer ones, use three AA cells. Hardwired detectors often have an AA or AAA backup.
Most common answer
If your smoke detector runs entirely on battery and is a single-module ceiling unit, it almost certainly uses a 9V cell. Remove it from the ceiling and open the compartment to verify.
How to identify yours if you're unsure
- Remove the detector cover (usually a quarter-turn counterclockwise or a slide).
- Look at the battery compartment label — it will state the type directly.
- Check the model sticker on the back for a manual reference.
Type comparison
| Detector type | Battery type |
|---|---|
| Simple standalone (ceiling mount) | 9V alkaline or lithium |
| Newer smart detector (Nest, Ring, etc.) | 3× AA or built-in sealed battery |
| Hardwired with battery backup | AA or AAA backup cell |
Relevant standard pages
Safety reminder
Replace smoke detector batteries annually, or any time the low-battery chirp begins. Lithium 9V cells last longer than alkaline in smoke detectors and are worth the extra cost.