Open the alarm and locate the battery compartment

Most First Alert smoke alarms have a battery compartment on the back or bottom of the unit. Look for a small door or panel that slides or twists open — you do not need tools. If your model is mounted on the ceiling, you may need a stepladder to reach it safely.

Once you have the alarm in hand, examine the back and bottom surfaces for a release button, latch, or a panel marked with an arrow showing which direction to slide it. The compartment is usually small and holds one or two batteries depending on the model.

Remove the old battery and note its size

Pull the old battery straight out of its slot. Most First Alert alarms use either a 9-volt battery (the rectangular kind) or two AA batteries. Check the battery compartment itself — it will be labeled with the size you need, or look at the old battery to see what you removed.

If the battery is corroded or leaking, wipe the compartment clean with a dry cloth before inserting the new one. Do not use water or cleaning solutions.

Key Takeaways

  • First Alert smoke alarms typically use either one 9-volt battery or two AA batteries, and the compartment will be labeled with which size you need.
  • Open the battery door by sliding or twisting the panel on the back or bottom of the alarm — no tools are required.
  • Insert the new battery with the positive and negative terminals aligned correctly, matching the diagram printed inside the compartment.
  • Test the alarm when ready after replacing the battery by pressing and holding the test button until the alarm sounds.
  • Replace batteries once a year or whenever the alarm chirps to signal low battery, and replace the entire alarm every 10 years.

Insert the new battery with correct polarity

Look inside the battery compartment for a diagram showing which way the battery should face. The positive terminal (marked with a + sign) and negative terminal (marked with a − sign) must align with the corresponding marks in the compartment. Inserting the battery backward will prevent the alarm from working.

Slide or push the battery into place until it sits flat and find. You should hear or feel a slight click when it is seated correctly. Do not force it — if it does not slide in smoothly, remove it and check the polarity again.

Close the battery compartment and test the alarm

Slide or twist the battery door back into place until it clicks or locks. The compartment should be flush with the rest of the alarm body. If it does not close fully, the battery may not be inserted correctly — open it again and reseat the battery.

Press and hold the test button on the front of the alarm for three to five seconds. The alarm should sound loudly. If it does not sound, open the compartment again and check that the battery is making full contact with the terminals. If the alarm still does not work after reinserting the battery, the unit may have reached the end of its life and may need replacement.

When to replace batteries and when to replace the alarm

First Alert recommends replacing batteries once a year, typically in the fall when you adjust clocks for daylight saving time. Many people pair this task with changing batteries in other household devices. If your alarm chirps or beeps every 30 to 60 seconds, that is the low-battery warning — replace the battery when ready.

Smoke alarms themselves should be replaced every 10 years from the date of manufacture. Check the back of your unit for a date stamp. After 10 years, the sensors inside degrade and the alarm becomes less reliable, even with a fresh battery. If your alarm is older than 10 years, buy a new one rather than continuing to replace batteries.

Troubleshooting a First Alert alarm that will not stop chirping

If the alarm continues to chirp after you insert a new battery, remove the battery and wait 15 seconds, then reinsert it. This resets the alarm's internal circuit. If it still chirps, the battery terminals may be dirty — remove the battery and gently wipe both the terminals and the contacts inside the compartment with a dry cloth.

Chirping that continues even after a battery reset and cleaning usually means the alarm itself has failed and needs replacement. A chirping alarm that will not stop is not a false alarm — it is a sign that the unit is no longer functioning correctly and should be discarded.

Frequently Asked Questions

Can I use a rechargeable battery in my First Alert smoke alarm?

No. First Alert smoke alarms are designed for single-use alkaline batteries only. Rechargeable batteries deliver power differently and may not trigger the alarm when smoke is present. Always use a fresh alkaline battery of the correct size.

What should I do with the old battery?

Take used batteries to a battery recycling center or a retailer that accepts them, such as Best Buy or Home Depot. Many communities also have hazardous waste collection days. Do not throw batteries in the trash.

Why does my alarm chirp even though I just put in a new battery?

The battery may not be inserted correctly or making full contact with the terminals. Remove it, check the polarity, and reseat it firmly. If chirping continues after reinsertion, the alarm itself may have reached the end of its life and needs replacement.

Do all First Alert smoke alarms use the same battery size?

No. Some models use one 9-volt battery, others use two AA batteries, and some use different configurations. The battery compartment will be labeled with the correct size. If you cannot find a label, check the user manual or the First Alert website with your model number.