For some reason, we're seeing a lot of spy gear making the rounds these days, and here's yet another, an eavesdropping device you can make yourself for less than $25. This guy has replaced the earpieces on a $10 stethoscope with condenser mics from a couple of cheap-ass multimedia microphones. Then it's no big deal to hook those up to the recorder of your choice, so you can have the proof you need. Take a look at the how-to video, after the jump.
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You can either go through these steps to have yourself this cut-rate spy device, or you could just use a stethoscope to listen through walls directly. Or how about this: You could just stop being such a nosy muthafucka and mind your own beeswax. [Instructables]