There are two very different products competing for the same shelf here, and buying the wrong type leads to real heartbreak. True GPS trackers like the Petivity unit give live, real-time location anywhere there is cell coverage, which is what you need for a dog that bolts fences or slips the leash on hikes. AirTag-style holders such as the Saker IP68 case are cheaper and need no subscription, but they only show a last-seen point relayed through nearby phones, useless in a rural field with no people around. We tested both kinds for location accuracy, how often the position refreshed, waterproof rating after submersion, and how honest the battery claims were. We also flag the platform lock-in, since several of these tags work only with iOS or only with Android. If your dog is a known escapee, pay for a real-time GPS unit and its subscription. If you just want to find a collar that slipped off in the yard, a Bluetooth holder is plenty. Match the tech to the risk.