On that note, about 20 years ago, there suddenly was an abundance of small cheap alarm clocks with DCF77 receivers available. Got one of these and totally overslept every couple months. I eventually got a second alarm and set it a few minutes before the other one, and sure enough eventually there was a day where the second one (so my original one) didn't ring its alarm. I didn't look at the clock so was not able to see what was going on, but at least knew it wasn't me.
years later when I long didn't use that clock as an alarm anymore, I had it in a spot where it wouldn't properly receive the DCF signal and I noticed that it would quickly lag behind after just a few days. So my theory at that point was that sometimes the clock just managed to fall behind enough in its old spot and then resync just when the alarm would've gone off, and there was no logic to account for this. ie the clock would compare the time to the set alarm exactly once a minute, but when the clock would receive a new time signal of 7:01:00 when its local time was 6:59:59 or earlier, I'd oversleep.
years later when I long didn't use that clock as an alarm anymore, I had it in a spot where it wouldn't properly receive the DCF signal and I noticed that it would quickly lag behind after just a few days. So my theory at that point was that sometimes the clock just managed to fall behind enough in its old spot and then resync just when the alarm would've gone off, and there was no logic to account for this. ie the clock would compare the time to the set alarm exactly once a minute, but when the clock would receive a new time signal of 7:01:00 when its local time was 6:59:59 or earlier, I'd oversleep.