Made of milled aluminium, the $US300 case (oof!) locks your iPhone in with sealed gaskets and a clear screen protector allowing you to still see the display and use your phone as a camera. There’s no access to the lock button, though, so you’ll need to disable autolock and keep it perpetually on before entering the water.
And since you can’t access its touchscreen either, you’ll have to put your iPhone’s camera icon at the bottom of the main screen so that it, and its shutter button, can be accessed using a series of touch-sensitive buttons built into the case.
It sounds like a bit of a pain to use, but when you surface again, you’ll be glad you can immediately upload all your photos to Instagram and commence bragging.