Here’s a rather interesting device that can tell you how much electromagnetic field are around where ever you may be, all cased in a retro-fitting style wooden box. I think this would be great to have around to test how much EMI your cellphone is producing.
This device uses a circuit that I constructed myself to detect electromagnetic fields. All flowing electricity gives off an electromagnetic field, with this device you can hear them all! They can be musical and harsh, the variety of electromagnetic sounds you can detect is limited only by the number of electronic doohickeys you own! As an added bonus it also detects ghosts.
Also check out this video of the device detecting internet EMI: