Me and my girlfriend went down to Newquay to surf this summer and this was the best purchase the whole holiday. Tied it round swim shorts/bikini in the wetsuit and was fine and kept car keys and money dry :)
I had one of these before and mainly use it for my phone when cycling.
I've also used it for car keys inside a wetsuit whilst surfing and keeps everything completely dry.
I lost the original so I've bought 2 this time in case I lose another!!!
Bought this for a friend's birthday and not sure if it has been tested out, so I can't say if it is completely waterproof, but the product looks top quality.