From my experience working as a dog walker there are two basic types of trackers for dogs:
1. Cell Service powered - domestic use
2. GPS powered - hunting, search and rescue, etc
The cell type is dependent on a cell network and towers, but has an unlimited range as long as there is service.
pros:
less expensive
unlimited range
cons:
dependent on cell service - wont work in boonies.
Monthly service required, usually 15-30$/month per dog.
The GPS type uses a GPS device and radio signals to communicate with the collar tracking device on your dog and can be used in remote areas.
pros:
Very reliable and accurate
Can be used outside cell service areas
Can track multiple dogs at the same time
cons:
Very expensive, 300-700$ depending on new or used and model type. (but no subscription to services needed)
Range is limited to 2-9 miles!!! When my dog was lost I found him 15 miles away from where we were separated. He ran along freeway and did not stop until completely exhausted.
Bottom Line: Both are best if you want to make sure your dog is found, but neither will ensure your dog will be found. Try to imagine what your dog would do if lost - is he a runner? a hider? Knowing whether your dog has a predominant flight or fight response is very important. Also any peculiarities and triggers should be on your red flag list. Be on lookout for things that can scare your dog or situations that can lead to separation such as vehicle break ins. Use leashes. If your dog is a specially high target for theft, be aware of other people. That happens, trust me.
