Always save the instructions that come with the alarms for testing and maintenance. Test alarms at least once a month by pushing the test button.
Smoke alarms with non-replaceable batteries are made to work for 10 years. If the alarm "chirps", warning that the battery is low, replace the alarm with a new one. For smoke alarms with any other type of battery, replace batteries at least once a year. If the alarm "chirps", replace the battery right away.
Replace all smoke alarms when they are 10 years old or if they do not respond when tested. Look on the back of the alarm for the date.
Replace combination sensor smoke/carbon monoxide alarms according to the instructions that come with the alarms.