I have a couple of Tile fobs from before Apple moved into the space. They're still good enough for checked bag tracking while flying (at least to confirm the bag has made it to the terminal). Tracking is pretty limited without the subscription, but enough to sanity check. It would also work as a "last seen" location, which might be enough for your example (you don't need the network unless your device moves).

Find My should also give you a push notification if you leave a device somewhere? But you'll get false positives if you turn off Bluetooth.