If you're changing the batteries on a hard-wired smoke detector, you should first shut off the power at your circuit breaker. On some models, you can just twist the cover off, while you'll need to snap the cover out of place on others.
In short yes. Hard-wired smoke detectors run directly from a circuit panel should be powered down to change. If they are run in series with other smoke detectors, all should be changed at the same for compatibility. No fun grounding out on live wires.
Just to add a bit of info I learned. With hardwired smoke detectors, when you change out the batteries, you also want your unplug the detector and hold the test button. You will often hear the detector discharge when you do that. Hold the button for like 20 seconds or so. Then reinstall the battery and plug it back in.
Edit: From experience with similar units releasing the battery does not require disconnecting mains wiring. When you release the base there should be enough slack to let you lift the battery cover lid and take the battery out. If you are unsure just turn the fuse board off completely before you do it.
To get the device to stop chirping once the battery has been removed, you must drain this residual charge by holding the test button for 15 seconds.
Remove the battery: If your smoke detector has a backup battery, remove it and press the test button for 15 seconds to drain any residual charge. Reinstall the battery: Insert a fresh battery and reconnect the power cable.
Turn off the circuit breaker for your smoke alarms. If your smoke alarms don't have battery backup, doing that will turn all of them off. If your smoke alarms have battery backup, go to the faulty smoke alarm, twist off the cover. Once the wires are exposed, carefully disconnect the smoke alarm.
Clear Residual Charge to Stop the Chirp
Remove the alarm from your ceiling or wall. Open the cover and take out the battery. Press and hold the test button for 15-30 seconds. This will fully reset the smoke alarm and drain any charge left inside.
Common reasons a fire alarms keeps going off are: Dead or dying batteries. Poor placement, like in kitchens, bathrooms or garages. Interference from airborne chemical compounds, like those released from wet paint.
Can I install a hardwired smoke detector myself? While it is technically possible, it is not recommended. Working with your home's electrical system can be dangerous and complex, best left to a qualified electrician.
Tip: Before working on a hard-wired smoke detector, turn off the main power at your circuit breaker to avoid electrical shock.
Disconnect the wire harness by squeezing the locking arms on the quick connector while pulling the connector away from the bottom of the alarm. Battery-operated alarms will not have a wire harness.
Perhaps you have a hardwired smoke alarm that is connected to your electrical breaker. If this is the case, you'll need to make your way to the electrical panel and look for a breaker labeled “Smoke Alarms” or “Central Smoke Alarm.” Turn the breaker to the off position and wait a few minutes before turning it back on.
Why did my fire alarm randomly go off in the middle of the night? This is likely due to one of the common causes like low battery, dirt buildup, humidity, or insects interfering with the sensor. Test the alarm and clean it thoroughly to try and resolve the issue. Make sure batteries are fresh and secure.
Stopping a smoke alarm from beeping is often simple. Get a step ladder and carefully reach for the alarm. Pressing the “Test/Silence” button on the front of the unit should stop it from beeping or chirping. If this doesn't work, grasp the device and turn it counterclockwise.
Stopping a smoke detector from beeping or chirping involves checking its batteries, cleaning it, or addressing environmental factors that may trigger the sound. If the problem persists, the unit may need replacing.
If you replaced the battery and it's still beeping, the smoke detector might have expired like milk. Smoke detectors have an expiration date. The sensitive equipment inside can only work reliably for so long, so if yours is beeping and its expiration date has passed (or will in a year or two), it's time to replace it.
Does the smoke detector need to remain connected at all times? Yes. Most importantly, if the smoke alarm in your property is disconnected, it could result in criminal charges if there is a fire on the premises.