Iphone hack: Type *3001#12345#* and then hit call

This brings up the Field Test app, where you can change the standard reception bars to decibels referenced to one milliwatt (dBm) for greaer accuracy when looking for a signal.

https://www.quora.com/What-cool-things-can-one-do-with-an-iPhone-and-iPad-that-most-people-dont-know-about

FanFootage.com