I did a much lower fidelity experiment this past week with one of my kids.

I have some radios I threw in metal boxes on the off chance something like this happened so we’d have some way to get emergency alerts. To check how well it shielded we threw my phone in it and they called to see if it rang. It did.

So we tried some other things - the microwave (worked), a tool chest (didn’t), a faraday bag (worked), miscellaneous storage boxes (didn’t).

Fortunately, the box with the radio was an old box and some paint had worn from the edges. We made a “seal” out of aluminum foil and tried again. It worked.

This only tested high frequency signals and probably doesn’t reflect real EMP risk in any way, but it was fun to do.

When you say "worked", do you mean the phone worked in the microwave or that the microwave worked as a Faraday cage and prevented the phone from ringing?