Granted it’s not the most tech savvy way of protecting your phones from your prankster friends, but assuming you get back to the table on time, you should be able to tell if someone’s held your phone recently. Thanks to body heat, whoever’s held your phone will have an imprint of their hand on the back of the casing which will show up in white. If this sounds familiar it’s because of the thermo t-shirts that were made popular back in the 80’s.
In any case (pun intended), if you’re a fan of novelty casings for your iPhone, the Incase Thermo Snap Case is said to be compatible with both the iPhone 4 and iPhone 4S and will be available for $35, so for the sake of novelty or perhaps nostalgic value, head on over to Incase’s website for more information or to pick one up for yourself.