For example, you can buy a wristwatch GPS receiver.

However, GPS has some real limitations. One of the biggest limitations is that the GPS signals are incredibly weak. My GPS units have trouble locking into the signals while inside my house. It doesn't take much to block them. That would limit their usefulness in a locator device.

How would a locator chip work, anyway? Would you broadcast a signal and hope for a response? Would it be passive or would it need some sort of power source?

Reminds me of a line from a "Buffy" episode:

Buffy: "Dawn is missing."

Spike: "Have you ever considered getting a Lojack for the girl?"