I used to work as a phone tester and sometimes had to test things while the phone was in a unreceivable location. I tried many things, like a safe, fridge, cook

I used to work as a phone tester and sometimes had to test things while the phone was in a unreceivable location. I tried many things, like a safe, fridge, cookie jar etc, but the only thing that worked was wrapping the phone in 2 or 3 layers of tin foil.