The PINA (personal intelligent nutrition aid), designed by Eric Chain, contains a sensor that evaluates the nutritional value of the food you're about to eat (within ten inches) and then lets you know if it's a good choice or not by emitting a series of gentle vibrations. It's supposed to be able to calculate carbohydrate, calorie, sodium, cholesterol and bacterial contents in food, so this is probably a non-working mockup, because I doubt there's any sensor (especially one this small) that could do all that at this time.
So you can't buy a PINA yet, but there's always the Powerseed (aka the 'seed), which is available now and helps you determine how full you are before you take another bite.
From Wrist Fashion.