[redleader55]

The simplest test you can make to verify that the microwave oven & biscuit tin can are good Faraday cages is to put your phone in one and try to call it - every time I did that in the past they failed to function as a Faraday cage.

Edit: clarification.

[jmnicolas]

Did you wrap your phone with something non conducting so that it doesn't touch the tin or microwave?

It works for me with a cookie tin, the phone is wrapped in a towel.

[OJFord]

That's an easy way to verify failure (phone rings) but not success - unless the only thing you care about blocking is phone calls I suppose.

[dzdt]

The Faraday cage failed (the phone rang?) or the phone failed to ring (Faraday cage succeeded)?

[redleader55]

Clarified the text of my original comment.