Step-by-step instructions on how to change smoke alarm batteries are provided at HomeTips. Additional important information about smoke alarms and how smoke alarms work is provided by HowStuffWorks and the United States Fire Administration website.
Smoke alarms are powered by batteries or by the home's electrical system. Smoke alarms built into the home's electrical system also have a backup battery. The battery equipped in a smoke alarm is either a replaceable 9-volt battery or a non-replaceable 10-year lithium battery. FEMA recommends that 9-volt batteries and back-up batteries be replaced once every year. 10-year lithium batteries do not need to be replaced until they wear out.