If the smoke detector emits a short beep every 40 seconds and the red LED lights up simultaneously, the battery is empty.
On the side of the detector you will find a small sticker with the text “Press a screwdriver into the lock and push the detector away from you”. You can unlock the secure lock here using a screwdriver (press the screwdriver slightly down).
Slide the detector off the base plate
Remove the battery and replace the 9V block battery
Place the smoke detector back on the base plate and click it into place.
Check carefully whether everything is connected safely! Switch the power back on (the green LED lights up again) and test by pressing the button on the smoke detector.