In F-Droid, there is an APP called findmydevice, which aims at replacing Google location services but find ones device if lost. In the past, the only possibility was to trigger the phone via SMS. Now, there is a possibilty to communicate to the mobile via server.
I don’t know, if that’s a realistic, but I guess it would be a really good idea to have a nextcloud APP as server vor this purpose! What do you mean, is it possible?
More Information on FindMyDevice you find here: