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What battery does a smoke detector take?

A smoke alarm takes a 9V battery, AA batteries, a CR123A or a sealed 10-year battery you don’t change, depending on the model.

Who made the alarm?

How is it powered?

The battery it takes

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Which battery, by model

Smoke alarm batteries by maker and model
AlarmPowerBattery
Kidde 20SDRBattery2 AA
Kidde 20SD10, i1040SealedNone to change
Kidde 20SARHardwired2 AA backup
Kidde i12060HardwiredOne 9V backup
Kidde 20SA10HardwiredSealed 10-year backup
First Alert SMI100BatteryOne 9V
First Alert SM2-B01, SC2-B01Battery2 AA
First Alert SMI110, SM2-B10, SC2-B10SealedNone to change
First Alert SMI100-ACHardwiredOne 9V backup
First Alert SM2-W01, SC2-W01Hardwired2 AA backup
First Alert SM2-W10, SC2-W10HardwiredSealed 10-year backup
Google Nest Protect (battery)Battery6 Energizer Ultimate Lithium AA (L91)
Google Nest Protect (wired)Hardwired3 Energizer Ultimate Lithium AA (L91) backup
X-Sense XS01-WRBatteryOne CR123A
X-Sense SD2J0AXSealedNone to change

From each maker’s product page or manual. The SC2 models are combined smoke and carbon monoxide alarms.

Find the model number first

The battery depends on the model, not only the maker. Kidde prints the model number and the date the alarm was made on the label on the back of the alarm, so take it off its bracket and look there before you get batteries.

A round smoke alarm off its ceiling bracket, seen from the back, with two lines of the printed label on its back circled.
Off its bracket, the alarm’s back carries the label with the model number and the date it was made.

9V, AA or a sealed 10-year battery

The U.S. Fire Administration (USFA) says a battery smoke alarm runs on either a disposable 9-volt battery or a nonreplaceable 10-year lithium battery. Some Kidde and First Alert models take 2 AA batteries instead.

A sealed 10-year alarm has no battery door, because its lithium battery is built in to last as long as the alarm. First Alert’s SMI100 manual says to use only the exact batteries it specifies.

Three round smoke alarms: one with a battery door open on its side, a sealed one with no door, and a hardwired one with a wiring plug on its back and a small battery door.
A battery door means a 9V or AA to change. No door means a sealed alarm. A wiring plug on the back means a hardwired alarm with a backup battery.

Hardwired alarms have a backup battery

USFA says an alarm wired into the home’s electrical system usually has a backup battery that needs replacing at least once a year. Which battery it takes depends on the model, so check its label.

When it chirps

Kidde and First Alert both describe a short chirp, repeated every 30 to 60 seconds for about a week, as their low battery warning.

A chirp can also mean the alarm is worn out. Kidde’s support page says its carbon monoxide alarms start chirping every 30 seconds seven years after they’re first powered, and each model’s manual gives its own pattern. See carbon monoxide detector battery.

Care, from USFA

USFA says to test every smoke alarm monthly and to replace a 9-volt battery at least once a year. Take care of each alarm according to its maker’s instructions, USFA adds.

Common questions

When should I replace the whole smoke alarm?

USFA says every 10 years for an alarm with a 9-volt battery or a hardwired alarm, and when the maker says for a long-life alarm. Kidde's sealed alarms chirp or beep to tell you.

Can I take the battery out if the alarm goes off while I'm cooking?

No, USFA says never to take the battery out of a smoke alarm while cooking.

Keep going

Batteries for home devicesWhat battery does an AirTag take?9 volt battery types

Where we get our information from

Batteries and chirps come from Kidde, First Alert, Google and X-Sense product pages and manuals, and care advice from the U.S. Fire Administration, all read on October 25, 2026. Checked against published data from Kidde, First Alert, X-Sense, U.S. Fire Administration and Google.

See all 17 sources
  • U.S. Fire Administration (FEMA), Smoke alarms
  • Kidde, Smoke Alarm, AA Battery Powered 20SDR (product page)
  • Kidde, Smoke Alarm, 10-Year Battery Powered 20SD10 (product page)
  • Kidde, Smoke Alarm, Hardwired with AA Backup Battery 20SAR (product page)
  • Kidde, Smoke Alarm, Hardwired with 10-Year Backup Battery 20SA10 (product page)
  • Kidde, AC Hardwired Smoke Alarm i12060 (product page)
  • Kidde Support, What Causes Consistent Chirping?
  • Kidde Support, How to Find the Date of Manufacture on an Alarm
  • Kidde, Micro 10-Year Sealed Battery Smoke Alarm i1040 (product page)
  • First Alert, SMI100 Smoke Alarm user's manual (M08-179721, PDF)
  • First Alert, SC2/SM2 Series Battery Powered Smoke and Combination Carbon Monoxide Alarms manual (900-00647-001, PDF)
  • First Alert, SC2/SM2 Series Hardwire Smoke and Combination Carbon Monoxide Alarms manual (900-00645-001, PDF)
  • First Alert, SMI100-AC Smoke Alarm user's manual (M08-179722, PDF)
  • First Alert, 10-Year Battery Smoke Alarm SMI110 (product page)
  • Google Nest Help, Replace Nest Protect's batteries
  • X-Sense, XS01-WR Wireless Interconnected Smoke Alarm (product page)
  • X-Sense, SD2J0AX Standalone Smoke Alarm (product page)

Battery sizes come from battery makers' datasheets and device makers' own manuals and help pages. Check your device's manual or the old battery before you buy. If anyone may have swallowed a battery, call the National Battery Ingestion Hotline at 1-800-498-8666 or your poison center at 1-800-222-1222 straight away.