How To Replace a Smoke Alarm Battery
If your smoke alarm is chirping every two minutes it probably means the backup battery is almost flat. Fortunately it's very simple to open the smoke alarm and replace the battery.
Note, if your alarm is connected to mains power, disconnect it at the circuit box before starting.
Follow the instructions on the unit. Insert a flathead screwdriver into the hole and press until the latch releases.
Push the cover away in the direction of the arrow.
If you're having trouble, there might be YouTube videos showing the angle of the movement which will show you how simple it is. If the smoke alarm doesn't move easily, it might need a love tap, or a bit of extra pressure on the latch.
Remove the battery. You may or may not have broken the latch by now. Either way, the cover is not budging. You can try to brute force it by leveraging it with the screwdriver.
It keeps fucking beeping. Your arms are fatigued and every two minutes the chirpy fucker sounds off right next to your eardrum. You've tried pushing, you've tried twisting. The only thing left to do is tear your way inside with a pair of pliers, tiny piece by tiny piece until you can release the latch.
Destroyed, it opens easily. Install the new battery. Finally, silence. Amazingly, the cover goes back on. Clean out the fragments of plastic from the carpet. Put the power back on.
You may find it more convenient to perform this step before step two.