ThinkGeek has perhaps one of the geekiest T-shirt available on the market: a WiFi detector shirt.
This t-shirt features a glowing animated image which displays if there's a 802.11b or 802.11g WiFi signal and it also shows the signal strength. The t-shirt is powered by three AAA batteries which should last for several hours according to the site and fortunately all the gadgetry is removable so you won't have to worry that the wash machine will destroy your ultimate WiFi god t-shirt.
Glowing animated shirt dynamically displays the current wi-fi signal
Shows signal strength for 802.11b or 802.11g
Black 100% Cotton T-Shirt
Animated Decal is Removable (with hook and loop fasteners) for Easy
Battery Pack is Concealed in a Small Pocket Sewn Inside the Shirt
Runs for hours off three AAA Batteries (not included)