Why is my smoke detector chirping? How to stop it, and how to test it

Chirp, alarm or end of life: what the sound means

A chirp and an alarm are different sounds. First Alert says three beeps and a pause is an emergency warning: smoke has been detected, so get everyone out and call 9-1-1 once you are safely outside. Kidde says that when an alarm detects smoke it gives a loud, continuous sound until the air clears. First Alert says never to ignore any alarm.

A chirp is the alarm asking for attention. NFPA says a single chirp every 30 or 60 seconds means the battery is low and must be changed, and that chirping that continues after the battery has been replaced means the alarm is at the end of its life and must be replaced. Kidde says a low-battery chirp comes every 30 to 60 seconds for at least seven days.

Some alarms use different chirp counts for different problems, so check the signal chart in your manual or on the alarm. On First Alert's SM300-AC hardwired alarm, for example, one chirp every minute means replace the battery, and 3 or 5 chirps every minute or so means replace the alarm. Kidde adds that an intermittent chirp with no regular pattern usually means the battery is starting to lose charge.

Why it always seems to chirp in the middle of the night

Kidde says the 3 a.m. chirp comes down to the battery's charge and the air temperature. As a battery nears the end of its life, a drop in room temperature raises its internal resistance, which can push the alarm into its low-battery chirp. Most homes are coolest between 2 a.m. and 6 a.m., so the alarm may chirp in the night and then stop when the house warms up a few degrees.

A chirp that stops by morning is still a warning. Kidde's advice is to replace the batteries in all your alarms and check how old they are: it recommends replacing all smoke alarms, battery and hardwired, every 10 years, and replacing them if you don't know their age.

How to stop a low-battery chirp

Replace the battery. The CPSC says that if your smoke alarm begins to chirp, signaling low battery power, you should replace the batteries immediately so your family is not left unprotected. Kidde says a loose or badly fitted battery is a common cause of random chirping, so check these points as you do it.

• Use the battery type the alarm calls for (it is on the alarm and in the manual).
• Snap the battery in fully so it cannot be shaken loose.
• If the contacts aren't making good contact, disconnect and reconnect the battery once or twice.
• On alarms with a front-load battery, close the battery door completely.
• Press the test button afterward to check the alarm sounds.

Still chirping after a new battery?

Two things can cause it. Kidde says the alarm's processor can hold on to an error, such as a weak battery, even after the battery is replaced, and a reset clears it (the steps are below). If a reset doesn't stop it, the alarm may simply be worn out: NFPA says chirping that continues after a new battery means the alarm is at the end of its life.

Many alarms let you quiet a chirp for a while. First Alert's SM300-AC can silence its low-battery chirp for up to 8 hours, and Kidde says newer Kidde units have a low-battery hush of up to 12 hours. These buy time to get a battery or a new alarm; they are not a fix, and the chirp comes back.

Kidde also points to the room itself. Humidity, steam and condensation can trigger random chirping, as can strong airflow from a heating or cooling register, ceiling fan or open window within three feet of the alarm. It says its smoke alarms are meant for rooms between 40°F and 95°F.

Hardwired smoke detector chirping after a power outage

Hardwired alarms run on your home's electricity and usually have a backup battery, which USFA says needs replacing once a year. The CPSC says alarms wired to the house with battery back-up still protect you during power outages, which is why the backup battery matters: during an outage it is doing all the work.

Kidde says power surges or interruptions can make a unit chirp when the power is restored. If the chirping doesn't stop after the power is back, replace the backup battery if it is replaceable, then reset the alarm using your manual's steps. Kidde adds two wiring checks: if chirping happens at the same time each day it could be a power surge, and if it starts when something else in the house is switched on, such as an exhaust fan or heater, move that device to an outlet on a different circuit or have an electrician investigate. A loose white neutral wire can also cause an echoing chirp from one unit to the next, which is a job for an electrician.

Some alarms show when they are running on the battery alone. On First Alert's SM110LED-AC, for example, the green light flashes once a minute when the unit is on battery backup.

How to reset a hardwired smoke detector

Reset steps differ by brand and model, so use the steps in your own manual. Turn off the power before you take a hardwired alarm down: First Alert's SM300-AC manual warns of an electrical shock hazard and says to turn off the power to the area where the alarm is installed before removing it from its mounting bracket.

Check your own manual first, because even Kidde's steps vary: another Kidde page says to hold the test button for five seconds, and sealed 10-year models have their own instructions. For a battery-only alarm with a removable battery, Kidde says to remove the battery, press and hold the test button, then reinstall the battery: it will chirp when the battery is first connected but should not chirp afterward. If the alarm keeps chirping after a reset, Kidde says it may be time to replace it, and to check the date code on the label on the back. Here are Kidde's steps for a hardwired alarm with a battery backup.

• Turn off the power to the smoke alarm at the circuit breaker.
• Remove the smoke alarm from its mounting bracket and disconnect the power.
• Remove the battery, then press and hold the test button for at least 15 seconds. The unit may chirp or alarm for a few seconds before going silent.
• Reconnect the power and reinstall the battery. Kidde says the unit will chirp once when the power is restored and should not chirp afterward.

Finding the right alarm on an interconnected system

When interconnected alarms go off together, only one of them sensed the smoke. Kidde says to find that initiating unit by looking for the one flashing red or green at least once every second while in alarm mode; hushing that unit silences all the others. If the alarm stopped before you could find it, Kidde says the initiating unit then flashes for 1.5 seconds every 10 seconds. First Alert's SM300-AC and SM110LED-AC have a latching alarm indicator that shows which alarms in the series were exposed to alarm levels of smoke; the manuals say this latch does not work when the alarm is running on battery power alone.

Some alarms help you find the one with a low battery. On First Alert's SM300-AC, for example, a low-battery latch flashes the green light 2 seconds on, 2 seconds off, which First Alert says is designed to help you identify which alarm needs its battery replaced. Your manual's signal chart lists what each light and chirp pattern means. On a hardwired system, Kidde says a loose white neutral wire can make a chirp echo from one unit to the next.

When you test interconnected alarms, First Alert says to test each unit individually and make sure all units sound when each one is tested.

Nuisance alarms and the hush button

If an alarm sounds while you cook or shower, USFA says not to remove the battery. Open a window or door and press the hush button, wave a towel at the alarm to clear the air, or move the alarm several feet away from the kitchen or bathroom. The Red Cross says never to disable a smoke alarm, even if you get nuisance alarms while cooking or showering, and to use the hush button instead.

Kidde says the hush feature on most alarms temporarily lowers the sensitivity of the smoke sensor for up to 10 minutes, and should only be used for a known cause such as smoke or heat from cooking: never if a fire is present, and only after you have confirmed there is no danger. If the smoke is dense, the alarm overrides the hush. First Alert says its silence feature does not disable the unit; it makes it temporarily less sensitive to smoke.

If nuisance alarms keep happening, look at cleaning and position. The Red Cross says to vacuum cobwebs and dust from your alarms monthly. NFPA says to install smoke alarms at least 10 feet from a cooking appliance and at least 3 feet from bathrooms with showers or tubs, air vents and ceiling fan blades. The Red Cross adds that if the problem persists, look for a different type of smoke alarm and make sure alarms are in the correct areas of the home. Our smoke alarm placement guide covers where they go.

How often to test smoke alarms

NFPA says to test smoke alarms at least once a month using the test button, and USFA, the CPSC and the Red Cross say the same. The Red Cross says the test button checks all the electronic functions and is safer than testing with matches, lighters or cigarettes. Some manufacturers ask for more: Kidde and First Alert both say to test weekly, so follow your manual if it asks for more often than monthly.

To test, press and hold the test button until the alarm sounds. First Alert says to step away when the horn starts, since the horn can harm your hearing at close range. NFPA says to replace any smoke alarm that does not alert when tested according to the manufacturer's instructions.

For batteries, USFA says to replace 9-volt batteries and hardwired alarms' backup batteries at least once every year, and the CPSC suggests doing it when you reset the clocks in the fall or spring. First Alert recommends every 6 months. Alarms with a sealed 10-year battery need no battery changes but still need testing.

Replacing smoke alarms every 10 years

NFPA says to replace all smoke alarms when they are 10 years old from the manufacture date. The date is on the outside or back of the alarm; if there is no date, replace it. Sensors wear out over time and may take longer to detect a fire, which is why NFPA says to replace alarms after 10 years, or sooner if they give an end-of-life warning.

Sealed 10-year alarms work the same way. NFPA says alarms with non-replaceable long-life batteries are designed to remain effective for up to 10 years from the date of manufacture, and that when the alarm gives an end-of-life warning you should replace the entire alarm right away. The CPSC says that after 10 years, the entire unit is disposable. First Alert's manuals say you must replace the alarm immediately once the end-of-life chirp starts; the chirp can be silenced for up to 8 hours, but it comes back.

Combination smoke and carbon monoxide alarms can wear out sooner. NFPA says to replace them according to the manufacturer's recommendations, and Kidde says its carbon monoxide and combination alarms should be replaced every 7 years. When you replace an alarm, our smoke alarm comparison lists dual-sensor, sealed 10-year and interconnected models.

Hardwired, battery or interconnected: the short version

Battery alarms run on a disposable 9-volt battery or a sealed 10-year lithium-ion battery, USFA says, and hardwired alarms run on your home's electricity with a backup battery. The CPSC says battery-only alarms are the simplest to install in older homes, and new homes typically have hardwired alarms; after 1989, new homes included hardwired, interconnected smoke alarms.

Interconnected alarms all sound when one detects smoke. NFPA recommends interconnecting all smoke alarms for the best protection, and says hardwired alarms can be interconnected by a licensed electrician, or you can install battery-powered wireless interconnected alarms instead. The CPSC says interconnected alarms are typically connected with a wire, but newer wireless technology connects them without wires. First Alert says interconnected units may give earlier warning than stand-alone units, since all of them sound when one detects smoke.

USFA says only qualified electricians should install hardwired smoke alarms, and that your city, county or state may require a specific type, so check with your local fire marshal. Where each alarm goes is in our smoke alarm placement guide.

What never to do

USFA says disabling a smoke alarm or removing the battery can be a deadly mistake. These are the official and manufacturer warnings in one place.

• Never take the battery out to stop a nuisance alarm (USFA, the Red Cross). If it chirps for a low battery, replace the battery right away (CPSC).
• Never disconnect the power from a hardwired alarm to stop an unwanted alarm: First Alert says doing so disables the unit and removes your protection.
• Never test with an open flame (First Alert). Use the test button, which the Red Cross says is safer.
• Never use the hush button if a fire is present (Kidde).
• Never paint over an alarm, and never clean it with water, cleaners or solvents (First Alert).
• Leave installing or rewiring hardwired alarms to a qualified electrician: USFA says only qualified electricians should install them.
• Never ignore an alarm. First Alert says ignoring one may result in injury or death.

If the alarm sounds for real

When a smoke alarm sounds, USFA says you may have less than 2 minutes to get everyone outside, so make and practice a home fire escape plan. First Alert's manual also says to keep at least one working fire extinguisher on every level and another in the kitchen; our fire extinguisher comparison covers the home sizes.