Smoke detectors must be present in a home, by law in some states, to keep your family safe by alerting them to the presence of smoke during a fire. Smoke detectors are also supposed to be in working condition, meaning they need to have working batteries in them at all times. A smoke detector can usually beep even without a battery.
For safety reasons, smoke detectors retain enough power to continue beeping even if the batteries have been removed. This will let homeowners know that there is something wrong with the smoke detector and that it's necessary to replace the batteries so the alarm can function properly in an emergency. Some smoke detectors may also be wired into the house's electrical wiring for emergency power when the batteries fail, which is why they are able to beep with no batteries.
Batteries can expire, and batteries that have been stored improperly may not work. Most smoke detectors will be able to identify whether the batteries are good or not. If the new batteries are bad, the smoke detector will keep beeping.
Homeowners should replace the batteries in their smoke detector at least twice per year to ensure the smoke detector will work properly. Waiting until the batteries are dead to replace them is unsafe, as the smoke detector may not have enough power to go off in a serious fire emergency.
The Test Button
All smoke detectors have a test button that should be easily accessible from the outside. If the smoke detector is without batteries, pushing the test button should still result in a beeping noise. Consult your smoke alarm's manual to see if you need to reset the smoke alarm using the test button after replacing the batteries, as this may stop frequent beeping.