Where smoke and carbon monoxide alarms should go, and when to replace them

Put a smoke alarm inside every bedroom, one in the hallway or area outside each group of bedrooms, and at least one on every level of the house, including a finished or unfinished basement. In a two-story home with bedrooms upstairs, that usually means one in each bedroom, one in the upstairs hall and one on the main level near the living area.

Mount them on the ceiling or high on the wall, away from corners where air does not move. Keep them several feet away from cooking appliances and bathroom doors, where steam and smoke from cooking cause nuisance alarms that lead people to pull the battery.

Interconnected alarms sound together. A fire starting in the garage or basement sets off the alarm in the bedroom at the other end of the house, often minutes before smoke would reach it. That time is the whole point of an alarm system.

Hardwired interconnected alarms are standard in newer construction and the most reliable option. Where running wire is not practical, wireless interconnected alarms give the same whole-house warning, and many can connect to an existing hardwired system through a bridge.

Check the manufacture date on the back of each alarm. Most makers call for replacement about ten years after that date, and many carbon monoxide sensors have a shorter life. An alarm that chirps after a fresh battery, or sounds for no reason, is often at the end of its life.

Replace the whole set at the same time when they are the same age, so you are not chasing one chirping unit after another.

Most false alarms come from cooking smoke and shower steam. NFPA 72 generally keeps smoke alarms about ten feet from cooking appliances, with photoelectric alarms allowed somewhat closer, and at least three feet from the door of a bathroom with a shower.

Moving an alarm a few feet often ends the false alarms without leaving the area unprotected. Taking the battery out is the habit that leads to a silent alarm on the night it matters.

Hardwiring interconnected alarms is easiest during a remodel or rewire, but older homes do not have to wait. Wireless interconnected alarms with sealed ten-year batteries link every alarm in the house without new wiring.

If you plan to rewire later, the wireless set protects the family now, and hardwired alarms can be added when the walls are open. Either way, every bedroom, every hallway outside bedrooms and every level should be covered.