I have recently bought a cat gps tracking device for my cat. PAW TRACK a UK company. linky
http://pawtrack.com/It is really quite good, gives a six metre circular area of accuracy, there is Wifi and GSM and a built in beeper used for looking for lost cats/collars.
Comes in a choice of colours as long as its black. about 50g in weight. Includes three collar adjustment attachments, two usb li-ion batteries, usb chargable.
The first years subscription is free, after that its a monthly charge of about GBP6.99. You can log onto your tracking page from any internet capable device and locate your cats position.
Support is fantastic from the makers. Altogether I am very satisfied. Also you could use it for tracking anything, from errant grandparents to children.