Alarms use a transformer for power – most are plug-in, some are hardwired. The most common reasons for AC failure, assuming the power is on in the rest of the building, are:
- Transformer is blown due to power surge
- Circuit breaker that controls the outlet needs reset
- Outlet is a GFCI or GFI that has the circuit breaker built into the outlet itself, and needs reset
- Transformer become unplugged from the outlet.
