I think the GPS trackers for dogs, et al, depend on using a cellular connection to transmit the coordinates. I think this is SMS but I didn't see it mentioned in the dog tracker article. There will be a sim chip to enable contacting the cellular network and a subscription fee. Some GPS trackers appear to answer a "call" so they only provide info when called; that doesn't seem to be too large a limitation; the app on the phone can place that call at whatever interval the user desires if the feature is in the software to do so. The more often the updates, the lower the battery life. Cell calls take a lot more power/energy than Bluetooth contacts do.
If the GPS tracker is using SMS then it needs to be authorized on the cellular network for the location it is in. This might be a problem for international flight.
The GPS trackers also need a line of sight to GPS satellites where AirTags need a nearby Apple cell phone.