When should I replace my smoke detectors?

Replace every smoke detector in the house at the 10-year mark from its manufacture date, which is printed on the back of the unit. Replace the battery once a year unless the alarm has a sealed 10-year lithium cell. Test every alarm monthly by pressing the button.

How do I tell how old my smoke detector is?

Twist the alarm off its base and look at the back. Every U.S. smoke alarm sold since the late 1990s has a manufacture date printed there, usually a small white or yellow sticker with a date in MM/YYYY or just the year.

Add 10 years. That’s the replacement date.

If there’s no date sticker, or the sticker is illegible, the alarm is old enough to replace on principle. Sensors don’t last forever. The National Fire Protection Association recommends replacement at the 10-year mark from the manufacture date on the unit, not from when you installed it. An alarm that sat on a shelf for two years before you bought it still ages from the day it was made.

Some newer alarms print a “replace by” date on the front of the unit. If yours does, you can skip the back-of-the-unit check.

Where should smoke alarms be installed?

The International Residential Code (IRC R314) and NFPA 72 agree on the layout:

• Inside every bedroom
• Outside each separate sleeping area (the hallway just outside the bedrooms)
• On every level of the home, including basements and finished attics

In a typical three-bedroom house, that’s at least five alarms: three in bedrooms, one in the hallway outside the bedrooms, and one on each additional level. Newer code requires that all alarms be interconnected, so when one detects smoke, they all sound. Hardwired alarms link with a third wire run between them. Battery-only alarms can interconnect wirelessly if you buy a set designed for it (First Alert OneLink and similar).

Mount the alarm on the ceiling at least 4 inches from any wall, or high on a wall 4 to 12 inches below the ceiling. Don’t put one within 3 feet of a bathroom door, a ceiling fan, a supply vent, or a kitchen range. Steam, moving air, and cooking smoke all cause nuisance trips.

If the house was built before the 2006 IRC update, you may have fewer alarms than current code requires. Adding alarms during a battery-replacement pass is a one-evening upgrade.

What kind of smoke alarm should I buy?

Two technologies, often combined in one unit.

Ionization alarms detect fast-flaming fires (paper, grease, dry wood) about 30 to 90 seconds faster than photoelectric alarms in those scenarios. Photoelectric alarms detect smoldering fires (couch cushions, mattresses, electrical insulation) about 15 to 50 minutes faster. The U.S. Fire Administration recommends having both types in the home, either as separate alarms or as dual-sensor units that house both technologies in one device.

For new installs, a dual-sensor alarm with a 10-year sealed lithium battery is the simplest answer. You get both detection methods, no battery to swap, and the alarm dies on the same timeline as the sensors (which is correct). Brand names you’ll see at any hardware store: Kidde, First Alert, BRK. A standalone dual-sensor unit runs $20 to $35. Interconnected hardwired units run $30 to $50 each.

A combination smoke and carbon monoxide alarm is worth it on the level with the bedrooms, since CO concentrations are highest while people sleep. A dual-sensor smoke/CO alarm runs $40 to $60.

Skip alarms that don’t carry a UL listing (look for “UL 217” on the back). The cheap unbranded ones at discount stores sometimes don’t.

Why does my smoke alarm chirp?

Three patterns, three meanings.

A single chirp every 30 to 60 seconds means the battery is low. Replace it. If the chirping continues after a fresh battery, the alarm has reached end of life and needs to be replaced entirely.

A continuous beep or alarm-pattern chirping with no smoke usually means a nuisance trigger: steam from a shower, dust kicked up during cleaning, or a kitchen splatter. Wave a towel under the alarm for 30 seconds to clear the air around the sensor. Press the hush button if the unit has one. If it keeps tripping with nothing obvious, the sensor chamber is dirty (vacuum the unit with a soft brush attachment) or the alarm is approaching end of life.

Three chirps in a pattern, then a pause, then three more, is the unit telling you it has detected smoke or is malfunctioning. Get out, then investigate from outside. Don’t reset a real alarm.

A long beep that won’t stop after a new battery, after vacuuming, and after pressing reset, is the alarm telling you it’s done. Buy a new one. The InterNACHI life expectancy chart lists 8 to 10 years as the standard service life for residential smoke alarms.

What goes wrong if I keep an old smoke alarm?

The sensing chamber loses sensitivity over time. By year 12 to 15, an alarm that still passes the button test (which only checks the electronics, not the sensor) may not actually detect a real fire fast enough to matter.

NFPA data on home fires: about 3 out of 5 home fire deaths happen in homes with either no smoke alarms or alarms that didn’t work. Working alarms cut the risk of dying in a home fire roughly in half.

Replacement is a small job for the size of the gap it closes. A 10-year dual-sensor alarm runs $25 to $35. A typical five-alarm house is under $200 in parts and a one-evening install. If one alarm has hit its 10-year mark, the others usually aren’t far behind. Pull them all, check the dates on the backs, and replace any at or past 10 years in one pass.

A note from Kempt

Smoke alarms are the part of the house most people only think about when one chirps at 2 a.m. Kempt logs the manufacture date of every alarm in the house, schedules the monthly test, and gives you a heads-up the month an alarm is due to be replaced, with the room location and the exact unit so you can grab the right one on the way home.