Someone I know won one of those WiFi detecctor t-shirts as a door prize the other day. The plate on the front of the shirt (the detector itself is a little box connected via cables to the front plate) actually works. It went all blue (no WiFi) in a known dead-spot and lit up (four bars out of five in the photo above) where there was a WiFi signal. I wouldn’t buy one myself. But, it is a great gag gift.