When should you replace smoke detector batteries?

Replace standard smoke alarm batteries at least once a year and test every alarm monthly with the button. The classic advice to do it when clocks change is useful mainly because it is memorable. If an alarm chirps intermittently, that is the low-battery warning, and yes, it will always start at 3am, because falling nighttime temperatures nudge a marginal battery below threshold. Sealed ten-year lithium units skip the annual swap entirely, which is why they are worth buying on replacement.

The part most households miss: the detector itself has an expiration date. Smoke alarms should be replaced entirely every 10 years, and carbon monoxide alarms typically every 5 to 7, because the sensing element degrades whether or not the unit still chirps and tests. Look on the back for a manufacture date; if it is missing or older than a decade, replace the unit now. Placement matters as much as maintenance: an alarm on every level, inside each bedroom and outside each sleeping area, and interconnected alarms, where one sounding triggers all, buy meaningful extra escape time. Never solve nuisance cooking alarms by pulling the battery, move the alarm or use one with a hush button.