Nothing, I've not found anything reliable enough to bother with.
Bluetooth tags or even NFC tags would do it if you have limited entrances/exits. Or, if the family are willing, you could set up geofences on their phones (realistically only accurate to a 100m+ or up to 1/2mi in some cases) and of no help if someone forgets their phone or it runs out of power. But honestly, it is all too much faff.
What I do intend is to create an arming script for when we are all out. Someone can simply flip a switch to arm and again to disarm. Possibly with a small bleeper on an ESP device near the front door.
