It's not wearable but I wish it would because this product has a perfect "reason why"*:
Theft at places of leisure like beaches and swimming pools is on the increase.
Combine that with the cost of items we use during relaxation like MP3 players, sunglasses, mobile phones, cameras and so on, and we have the potential for significant loss.

The product called Yelpie and produced in the country of beaches is an electronic safe perfect for summer days at the water. The main feature could be build into clothes as well (but I bit adjusted):

Any attempt to move the device will result in a 90 decibel alarm sounding which will attract a lot of attention. Yelpie's clever design means that an accidental bump will not set it off. It needs repeated movements over less than a second to go into alarm. Once in alarm, it can be silenced (and unlocked) by entering your PIN.

Such a safety feature build into my jacket would be useful not only at the beach but at travels, airports etc. too.

Yelpie Product Page

via Lockergnome and RealTechNews --- read the comments there to learn how to better the "user interface" ;-)

* Advertising slang for: why should s/o buy it