When should I replace my smoke alarm?

The U.S. Fire Administration says smoke alarms need to be replaced 10 years from the manufacture date, and Massachusetts fire officials point people to the manufacturing date printed on the back of the alarm. It is the made-on date that counts, not the day you put it up. Test every alarm once a month with its test button.

Carbon monoxide alarms wear out too. Many print a replace-by date on the label; if yours does not, CPSC's general advice has been to replace CO alarms every five years, and the maker's manual gives the exact life.

Vigil works out the replace-by date from the made-on date, keeps a list of the alarms in your home, and saves a calendar file with a monthly test reminder and each replace-by date.

Help: grapnel.team@gmail.com