ZoomBak A-GPS Locator for Dogs

(And it seems to me that if you could use it for dogs, you could use it for cats as well — assuming that the hardware’s not too big.)

They also do locators for cars, bikes, family members, backpacks, etc. The devices report in via mobile phone, using the T-Mobile network and networks of the company’s roaming partners. (The coverage map doesn’t make it clear whether this coverage extends outside North America.)

Interesting…