A smoke detector not only alerts a person of the possibility of a fire in a home or office, but it also alerts the homeowner when it receives insufficient power from its main or backup power source. When you remove the backup battery or batteries from your smoke detector, the unit may beep if designed to alert you of the missing backup power source. This is a safety measure to remind you to replace the battery or batteries before you forget. To stop the beeping, you usually only need to replace the old battery or batteries with new.
Open your smoke detector battery compartment.
Insert your new battery or batteries into the compartment with the polarity marks in the unit lined up with the marks on the battery or batteries. If the unit has wires with connector-style contacts, snap the connectors in place on the appropriate matching terminals on the battery/batteries and then push the wires and battery/batteries carefully into the battery compartment.
Slide or snap the battery compartment cover securely in place on your unit. If the cover locks in place with screw(s), reinsert and secure the screw(s) on the cover.
Push the smoke detector reset or test button, or turn off the circuit breaker to the room where the unit is mounted to the ceiling or wall, to reset the unit. If your unit doesn't require reset to turn off the alarm after battery replacement, skip this step.
If your smoke detector continues to beep after you've inserted a new battery or batteries and/or reset the unit, reopen the battery compartment cover and check again that the battery terminals connect and that you matched the polarities properly. If the terminals don't connect or the polarities don't match, the unit may not recognise that you've replaced the battery/batteries. If the detector continues to beep, clean it. Unhook the unit from the ceiling or wall without disconnecting any main wires. Blow dust and dirt from the inside of the battery compartment, the exterior cover and along the edge between the cover and the back plate with compressed air--or vacuum the dust or debris away with a vacuum. If the problem persists, hire an electrician to inspect the unit and main electrical wiring leading to the unit as a malfunction is occurring, either in the unit or in the wires leading from the main power source.
Not securing the battery compartment cover can also cause the unit to beep.