I recently bought a whistle, which costs $80 and $100 a year. One charge lasts 6 days and it connects to your home network to save power. When your dog leaves your home wifi, it will start tracking using GPS and Cellular triangulation. It updates every 6 minutes but when your dog is lost, you can put it in track mode, refreshing every couple seconds. I find it very accurate and really cool, especially when you have a dog that needs to be outside a lot. Another cool feature is being able to track your dog's activity. You set a goal for them and then it tracks them to see if they complete it. It definitely made me more aware of taking my dog on walks. All in all, if you are an owner of an active dog who runs away a bit, this is for you. If you just want an activity tracker, this can function as one if you don't renew the GPS contract.
Link to it on Amazon: https://www.amazon.com/Whistle-GPS-Tracker-Activity-Monitor/dp/B01N7MWKWY/ref=sr_1_2?ie=UTF8&qid=1518293267&sr=8-2&keywords=whistle+pet+tracker