People are actually opting to buy this. From the NewScientist story:
Cristina, 28, who did not want to give her last name, was implanted along with seven other members of her family last year as a preventive measure. "It's not like we are wealthy people, but they'll kidnap you for a watch. Everyone is living in fear," she says. The chips cost US$4,000, plus an annual fee of $2,200.
Most people get the chips injected into their arms between the skin and muscle where they cannot be seen.
It's easy to see the motivation to buy the device -- this Reuters story says "official" government statistics peg the number of kidnappings in Mexico last year at 751, but independent researchers estimate those numbers probably exceeded 7,000.
While some technologies can certainly enhance security, this one isn't one of them. It's a clunky design, requiring both the implant and the GPS transmitter, and is too easy for criminals to circumvent. Consider the anti-carjacking technology LoJack -- that technology reduces the risk of carjacking for everyone because would-be carjackers don't know which autos are LoJack-enabled and which aren't, thereby making it a gamble to steal any given car.
All these implants are going to do is guarantee that those kidnapped are instantly handcuffed and strip-searched for the handheld device, and bolster Xega's ability to profit on fear.
Should I ever become kidnapped, the first place I'd likely tell the world is in on my Twitter-stream on Twitter, where I also often post security observations throughout the day.