Most iPhone users are afraid to get even a drop of water near their phones, lest they one day be rejected by an Apple Store Genius. But when strapped into the iGills waterproof case, you can safely dive with your phone to a depth of 130 feet, and keep track of when you need to surface.
Not only does the clear polycarbonate case turn your phone into an underwater video and still camera with a reinforced glass lens porthole on the back, it also includes a built-in depth and temperature sensor. And since you don't have access to the iPhone's touchscreen display or any of its buttons while submerged, the iGills has a set of its own that can be used to operate an accompanying all-in-one app.
So in addition to snapping pics, the app lets divers keep track of their depth, their time underwater, their nitrox levels for making safe ascents, and even alarms alerting them to their remaining oxygen supply. Since it doesn't actually tie into an oxygen tank or other external sensors, before you dive you have to explicitly program the app with various parameters so it can keep track of your progress. But for just over £210 ($330) it replaces a lot of other expensive dive gear. Not to mention ensuring you can check Facebook the second you surface. [iGills via iLounge]