The no subscription thing is going to be a hard thing to do. There may be ones that don’t cost anything but you will still have to make an account with the company to use.
What I would do is search for a GPS tag system and then see if some have HA integrations.
There are some Samsung ones or even random 3rd party ones.
I don’t know enough about the to give you more help, good luck and hope you get what your looking for.