What powers a smoke alarm?

Smoke alarms are powered by battery or they are hardwired into the home’s electrical system. If the smoke alarm is powered by battery, it runs on either a disposable 9-volt battery or a non-replaceable 10-year lithium (“long-life”) battery. A backup battery is usually present on hardwired alarms and may need to be replaced.

These batteries must be tested on a regular basis and, in most cases, should be replaced at least once each year (except for lithium batteries). See the Smoke Alarm Maintenance section for more information.

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1. Why should I have a working smoke alarm?
2. What types of smoke alarms are available?
3. What powers a smoke alarm?
4. Are smoke alarms expensive?