@feld @Moon @a1ba Also when I worked there my boss started hearing "beeps". One beep every few hours. He made a fuss about it because he thought some UPS was giving out or something (especially since we had makeshift server room right in there).
For quite some time we thought he was just being the mean motherfucker we knew him to be. Then I heard the beep one day as well.
We searched but found nothing. Beeps kept coming, about one per day. Every now and then the boss used them as an excuse to lash out at someone. This went for months.
Then we had to move and when they took out the furniture I found old Motorola phone someone dropped behind the table. It didn't have sim and was extremely low on battery and apparently when it was low on battery it beeped at increasingly longer intervals.