Most battery-powered smoke detectors use either a 9‑volt battery or two to three AA alkaline batteries, while many newer models have a sealed 10‑year lithium battery you never replace.

Common battery types

  • 9‑volt alkaline batteries were the standard for years and are still used in many older or basic smoke alarms.
  • Two or three AA alkaline batteries are now very common in newer detectors because they hold roughly three times more energy than a 9‑volt, so they can last longer between changes.
  • Sealed 10‑year lithium batteries are built into many current “10‑year” alarms; the whole unit is replaced when the battery reaches end of life.
  • Some smart or higher‑end alarms use lithium CR123A (123) cells, typically lasting about 3–5 years depending on how “smart” features are used.

How to know which you need

  • Check the writing on the smoke detector’s back or inside the battery compartment; it will specify the exact battery type and quantity required.
  • If the alarm is labeled as a 10‑year sealed model and has no obvious battery door, it uses a non‑replaceable lithium pack and the unit must be replaced at end of life or if it fails.
  • Hardwired alarms often still have a backup battery (usually 9‑volt or AA), so even if it is wired into house power, you still need to replace that backup.

Replacement and safety tips

  • Use quality alkaline batteries of the type specified (or the manufacturer’s recommended lithium cells) and avoid mixing old and new batteries.
  • Test your smoke detectors monthly and replace loose or weak batteries as soon as you hear chirping, which signals low power.
  • Many safety organizations recommend changing replaceable batteries about once a year, often when clocks change for Daylight Saving Time, even if they are not yet chirping.

Mini “forum style” note

If you’re standing under the alarm wondering “what kind of batteries do smoke detectors take?” the real answer is: it depends on your model, but 9‑volt, AA alkaline, or sealed 10‑year lithium are the big three.

TL;DR: Look at the label or battery door on your unit; most take either a 9‑volt or 2–3 AA alkaline batteries, while newer 10‑year alarms have sealed lithium packs you do not replace.