I'd consider it a hoax for a number of reasons.
1). Physical Size. GPS has very low Effective radiated power, that implies a need for an antenna on the order of 1/4 wave. At 1500Mhz, 1/4 wave is about 5cm, so an antenna with the largest dimension appreciably less than 5cm isn't workable.
2). GPS involves a substantial signal processing capability, that requires power. These are complex chip sets. If you look at the Casio GPS watch, even with a batter larger than the entire package, it gets about 2 hours battery life, and that is without a transmitter. It drives an LCD, but LCD's are static devices, they need trivial power.
The Casio is pretty close to the lower limit on GPS receiver size.
In short, there are serious mismatches between the antenna requirements for GPS, the power requirements for a GPS receiver, the physical size of the receiver, and the power requirements for a transmitter. This of course completely ignores the fact that the entire assembly needs to survive a 100+g acceleration while inside that tiny package, and the deceleration it gets when it hits someone/something.