Because you can't take the fridge with you on a false trail, place the phone inside at some point before deviating to the true meeting point, and then pull it back out again once the meeting has been completed and sufficient distance has been traveled.

Even some sort of electromagnetic shielding case or bag wouldn't be as convenient (so more likely to be used) or informative.

Yeah. Or have a little metal case with you into which you put your device. Or buy a roll of aluminum foil and just wrap the phone inside it (just spelling this out makes me feel like a conspiracy theory nutter). So many cheap options...

There are fairly cheap little faraday cage forensic bags that LEOs often purchase in bulk. Power off phone, slip phone in, it's not transmitting any more.

The introspection/detection part. That's the only part, actually. It doesn't stop the signals by itself.

Using this thing, you will know that you've been compromised if a transmission occurs. Fridge won't tell you that.

Knowing you are compromised, you could prepare disinformation to throw off, embarrass or otherwise humiliate an adversary.