Hard-wired smoke detectors also contain batteries as a backup plan. A battery ensures the alarm still functions even in the event of a power outage. The alarms beep or chirp if the battery is low to alert users to replace the batteries.
As of 2015, current building codes require smoke detector alarm systems to be hard wired into the dwelling's electrical system, but also require the battery backup. Batteries in these systems should be replaced once a year, and the entire system should be checked once a month. Fire protection specialists recommend replacing entire systems every eight to 10 years.
Hard-wired systems should be connected to each other. This ensures that the entire system sounds off when one alarm is activated, creating an alarm that can be heard throughout the dwelling. Systems should consist of a smoke detector in multiple places throughout the dwelling: one on every level, including the basement; one in every bedroom; and one in the kitchen and common areas.
Malfunctions can make the system sound off in a false alarm, and these occurrences can be seen as tests for the system. When a false alarm happens, the system can be reset with the push of a button.