My z-wave temperature sensor works inside my refrigerator. It's a stainless steel refrigerator with no window or icemaker in the door. Not sure how the signal gets out but it works.
Stainless is not a very good conductor. If it were aluminum or copper there’d be a problem but you can literally bury a bluetooth transmitter in a 16-gauge steel box with very little attenuation. I’ve done so at work.
