Someone once came to us and asked us to design a wireless thermometer for a freezer. We told them it wouldn't work, because the freezer would act like a Faraday cage. Then they showed us a similar device that worked just fine. Embarrassing.

We test a production device here that makes a LOT of noise, and we put it inside a mini-fridge to dampen the noise so it doesn't drive the testers crazy. Works quite well. I doubt you'd pick up any outside conversation if you were trying to eavesdrop (especially if the freezer was humming).