Neo coolcam doorsensor loosing connection

I have a few neo coolcam doorsensors. One of them is working outside to tell me when the mailman has come; works like a charm.

I am trying to set one up inside to warn me of the kids leave the bathroom door open. For some reason I cannot get the sensors to continie to work, I habe tried another one (I ordered three), the third one gives the same issue as the first one:

I can add the sensors fine, on the location where they need to be, they also work then. I see the status in the app changing and the red light also flashes when i move the magnet away from the sensor.

About 10 to 20 seconds later the whole thing stops working. No red light, no activity in the app… pressing the inside button -once- wakes the thing up and it works again for a few seconds.

Resetting (10 sec hold) does not change this. Removing and re-adding also does not help.

I would think the sensor is faulty but because I have it with two of them I am thinking I might be doing something stupid…

Anyone any idea ?

Thanks for your quick response !

Homey reports the battert as 100% full… Sorry to say that I do not have a volt meter…

Is it logical that it would work for a couple of seconds after pressing the button ? If so Ill just buy a new battery, probably cheaper then a vault meter…