I was asked to look into a beeping in a server room which no one could find.
It was understandably difficult as there were three server racks with modems, routers, switches, servers, PCs, UPSs, CCTV, and audio equipment. To add to that they were single beeps, quite wide spread apart, and within a noisy, concrete room. I determine after a little while they were single beeps and exactly 15 minutes apart. Typically first suspicions are the UPS units, but 15 minutes is not typical of APC UPS devices. To make a long story short, it turns out in a far corner where 2 fiber internet connections entered there were small UPSs units supplied by the service provider. One of the UPS units showed a failed battery. Being behind the open steel door, no one had seen the light.
This seems like a trivial post and an obvious solution but I am posting as there are many forums on the Internet with people not being able to locate a device creating a beep every 15 minutes. This is common with FIOS, Verizon, and Bell equipment. One story goes as far as to explain a fellow turning everything off in the server room, one device at a time, every 15 minutes, till everything was shut down and unplugged, but could still hear the beeps.