Airtag is a tiny accessory of apple which connects with iphone and shows its position through cell phone network.
It works with a small battery.
You can buy seperately a keyring where it fits perfectly.
🐾You can use directly airtag on a special collar or on the keyring on your furry friends.
Any moment you can open the app "find " and you can see your pets position on the map.
It is not that expensive and if you dont have an iPhone you can ask a favor of a friend!