[kurthr]

I'll confirm this works very well for 3G (600-900MHz) although I cut the hot off the plug out of paranoia when using one this way. Some of the 4&5G bands are up above 3GHz where it won't work so well.

Since your WiFi signal, however is almost exactly the same and there are many apps that will show and record signal in dB (as described in TFA). You could measure while the door open/closed if you're really careful not to turn it on. The lithium battery fire could respond very badly to water!