How to test, replace and add smoke alarms
Smoke alarm placement means one inside every bedroom, outside each sleeping area and on every level, including the basement. Press each test button, then check the manufacture date on the back. Replace any alarm 10 years past that date, and keep alarms at least 10 feet from the stove.
Smoke alarm types and power sources to choose from
Every alarm you buy should be listed by a nationally recognized testing lab. After that, your choice comes down to the sensor and the power source.
| Type | What it's good at | Best use |
|---|---|---|
| Ionization | More responsive to flaming fires | Use with photoelectric, or buy a dual-sensor unit |
| Photoelectric | More responsive to smoldering fires | Near kitchens and bathrooms, where it cuts nuisance alarms |
| Dual-sensor (both) | Covers both kinds of fire | Bedrooms and hallways, per USFA's advice to have both |
| Multi-criteria | Packaging says it "helps reduce cooking nuisance alarms" | NFPA suggests considering it when you replace an old alarm |
For power, a 9-volt alarm needs a new battery at least once a year. A sealed 10-year alarm has a battery you can't replace, so the whole unit goes when it expires. Hardwired alarms also have a backup battery to change at least yearly.
If anyone at home is deaf or hard of hearing, add a listed alarm with a strobe, or a pillow or bed shaker that works with your smoke alarm.
Where to put smoke detectors in your home
The rule of thumb from NFPA and USFA is inside each bedroom, outside each sleeping area, and on every level, basement included. Fit each one on the ceiling or high on a wall. Then check the manufacturer's instructions, since the best spot varies by model.
Keep alarms at least 10 feet from the stove, and out of the kitchen and bathrooms. Steam and cooking smoke set them off, and false alarms tempt people to disable them.
Interconnected alarms are the best setup, because when one sounds they all sound. That matters most with a closed bedroom door or a second floor. NFPA notes a qualified electrician can install them. If you add to an existing hardwired system, check that the new units are compatible. Your state or town may have its own rules, so ask your local fire department.
How to test a smoke alarm and fill the gaps
- Walk the house and map every alarm
Sketch each floor and mark bedrooms, hallways and existing alarms. Gaps show up fast.
- Test each alarm
Press the test button and listen for the loud beep, beep, beep. Test every alarm, whatever powers it.
- Read the date on the back
Twist each alarm off its base. Replace it if it's more than 10 years past the manufacture date, or if you can't find a date.
- Fresh batteries
Put new batteries in anything that takes them, including backup batteries in hardwired units. If a hardwired alarm has to come off its wiring, turn off the circuit first or call an electrician.
- Fill the gaps
Add alarms until each bedroom, sleeping area and level is covered. Stay at least 10 feet from the stove.
- Learn the sounds
Three loud beeps in a row means smoke or fire: get out, call 911 and stay out. A single chirp every 30 or 60 seconds means a low battery.
- Set a monthly reminder
Test each alarm once a month, and clean it following the manufacturer's instructions.
How many smoke alarms to budget for
| Item | What it costs | Notes |
|---|---|---|
| Battery or 10-year alarm | Varies by brand and sensor | Budget per alarm, then count bedrooms, hallways and levels |
| Replacement 9-volt batteries | Low; at least one per alarm per year | Hardwired alarms need these too |
| Hardwired or interconnected install | Varies; get an electrician's quote | Only qualified electricians should wire these |
| Alarms for deaf or hard of hearing people | Varies | Choose lab-listed products |
Smoke alarm placement and upkeep mistakes to avoid
- Assuming the seller's alarms work. NFPA says roughly three of every five home fire deaths happen where alarms are missing or don't work.
- Counting from when you bought the alarm. USFA and NFPA count the 10 years from the manufacture date.
- Treating every chirp as a low battery. A chirp that continues after a new battery means the alarm has reached end of life.
- Removing a battery to stop nuisance alarms. A dead or missing battery is the same as having no alarm.
- Wiring a hardwired alarm yourself. Turn this one over to a qualified electrician.
What homeowners say about when to replace smoke alarms
If you want warning of a garage fire, owners point out that a smoke alarm in the garage gives false alarms from car exhaust and dust. A heat alarm is the usual choice there. One owner added alarms to the garage and laundry room after a garage fire. (Reddit)
Ask your local fire department before buying. A volunteer firefighter says many stations give smoke alarms away free. Low-battery chirps tend to start around 3 a.m. as the house cools, so have spare 9-volts and a ladder that reaches your highest alarm before night one. (Reddit)
Hardwired alarms still have backup batteries that chirp when low, and owners say store batteries can already be old. Swap every backup battery on the same day and write the date on each alarm so they don't start failing one by one. (Hacker News, DIY Stack Exchange)
Smoke alarm placement questions
How many smoke alarms does a house need?
At minimum, one in every bedroom, one outside each sleeping area and one on every level, including the basement. A three-bedroom, two-story house with a basement can easily need six or more.
Why is my smoke alarm chirping after I changed the battery?
NFPA says chirping that continues after a new battery means the alarm is at the end of its life. Replace the whole unit.
Should I put a smoke alarm in the kitchen?
No. NFPA says not to put smoke alarms in kitchens or bathrooms, and to keep them at least 10 feet from the stove. If one must sit near a kitchen, photoelectric is the better type.
What you’ll need
Sources: NFPA, U.S. Fire Administration, CPSC
General guidance for U.S. homes, not professional advice. For gas, electrical and structural work, call a licensed pro.