When I started a new job at a NOC, I was pranked with one of those. I didn't know what to make of the odd recurring ~12khz beeps, and figured it was some old device slowly dying. So I pulled out a stopwatch to see if I could suss out the interval on the beeping. I was too focused on timing the beeps to notice my coworkers exchanging glances with each other after asking them, "Does anyone else hear that?"
I found a pattern emerge. It repeated itself every 10 beeps or so, with irregular intervals between those beeps. Armed with that information, I could effectively predict the next beep within 3-5 seconds (intervals ranged between 3-10 minutes, if I recall.) So I started walking around the room, standing in different locations as I stared at my stopwatch. The farther apart the places I stood, the better chance I'd have of triangulating the source with each beep.
I got within 3-5 feet of it in the ~300 square foot room before the coworkers came clean about what they had done. I wasn't even mad, I was having a blast!
