How often should you change smoke alarm batteries?
Once a year.
Best month: November (Northern Hemisphere)
How to do it
Swap the battery in every alarm that takes one. Sealed 10-year alarms have no battery to change; replace the whole unit when it chirps.
Why it matters
The low-battery chirp tends to start at 3 a.m. Doing them all on one day avoids that.
Recommended interval: once a year, per U.S. Fire Administration.
General guidance for a typical home; the manufacturer's instructions come first.