Good evening. What exactly are you looking to use this tracking device for?
If you are using the device to track your child, my research has shown that the Worldtracker GPRS is one of the best, XXXXX XXXXX rated tracking systems. Here is a link to the tracker's website, containing more detail, and purchase information: http://www.trackingtheworld.com/wtgprs.htmhttp://www.livestrong.com/article/254278-gps-tracking-devices-for-kids/
Pardon me, this is the link to the actual tracker: http://www.trackingtheworld.com/wtgprs.htm
This link is to an article that reviews the Worldtracker GPRS system, and other trackers that are good to use for children. I hope this helps. Feel free to contact me if you need more help.