Tagpo

Add your Bluetooth Low-Energy tags/devices to your list, give a name to
each one, and later you'll be able to run a scan and find which tags are
still around and which ones are missing (or not broadcasting).

For example, if you are a tour guide, and your group of tourists is
leaving the bus for some free time, after which you'll have to make sure
that everyone has returned. Just give each tourist a smart Bluetooth
button (that you added to the app beforehand), and when the time comes,
tell everyone on the bus to press their button, and you could easily find
out if anyone is missing.

To add more than 7 tags, you will have to purchase a subscription.