It did stop working, but then started working today? Although I do have a NOX sensor fault, that i’ve been told could cause the stop start to not work.
As AMgeed suggested a leaking internal battery within the alarm is more than likely the cause, I had similar problems and removed the fuse from the rear SAM until i got a replacement.
Easy job to remove the front nearside wheel and liner then it's plug and play
There should be a fuse map in one of the fuse boxes. Each fuse is numbered and the fuse map will tell you what each fuse does and where it can be found.
If you can find the fuse map, trying googling “fuse locations” and add the model of your car to the search.
The wifes SLC alarm went off a few times late at night, we had a look inside the car and there was a large spider which we removed, alarm never went off again.
My C class alarm started going off a year later, again at night time, this time we found a mouse had moved in!