I bought this thing: http://www.thinkgeek.com/gadgets/electronic/8c52/ I put it in my Lt's office above his computer under a book shelf. It makes a beep every 2 to 5 minutes and is impossible to find. I was in a meeting, it beeped, he started checking cell phones, computer, pager, desk recorder and going nuts. "Did you hear that?" He's pulling his office apart telling me its driving him crazy over the past few hours. Best $10 I spent.