The Eufy tags can be linked with the eufy security app or apple’s FindMy app, so he could link the device to his phone \ app then share location of it, rather than himself.
The slim card shaped wallet version is especially useful!
I appreciate your reasons but as others say, your son has been an adult for a number of years now. The downside of a consenting tracking method is your son may be more likely to let their guard down thinking “it’s OK, Dad has my back”. It’s then he is at more risk despite your best intentions.
If they’ve got enough sense to use Android instead of getting ripped off and locked in by Apple, I’m sure they’ll manage the challenge of driving on the other side of the road (and Channel) perfectly well.
If he’s okay with the tracking, it seems odd to restrict it to just the car - what if he goes for a 5 day hike, or off clubbing, he won’t be near his car. Or if they decide to take a quick flight to somewhere for a few days of lazing by a pool/watching a Grand Prix/whatever, then his car will be at the airport for a week…
Much easier and better and more reliable to share location using Google maps and leave it at that. Works for all Android and Apple phones.
If he’s not happy with the tracking, then you shouldn’t do it at all… And you should check whether she’s ok with you knowing where they are too, as she might not be okay with it.
It’s always tough to let people go off, and modern tech is a great way to retain the links. But another possibility is to discuss with him a weekly check in where he gives a quick call to update you. Or you could become a friend on Instrgram/Facebook if he’s planning to post on there, as you’ll see he’s still active…