[franga2000]

While definitely not as cool, this might be achievable with the same indoor positioning method the c3nav app uses, which would probably be accurate enough to track larger items at least to a few meters. After that, you can hopefully spot them easily, or maybe even use Bluetooth hot-or-cold to track them down further.

An ESP32 with a battery controller (wemos clone) + a little pillow cell would be around 6€ each (less if you buy in bulk).

[namibj]

1) It's actually not that good, sadly. 2) It's not up that early, as it depends on much of the networking to be set up before the WiFi works. The UWB system would be set up in around 1-2 hours just walking around with a load of wall wart/radio unit pairs and plugging them into sufficiently convenient outlets around the facility. They self-organize by ranging each other, and then you just take a device with UWB and RTK-GPS that's hooked up to the free (login-walled, but free) synthetic reference station service from the state's surveying bureau, and range in the fine locations of the base stations from a few points by pretty much just walking around the building's perimeter/fresh-air-access-doors to catch both GPS and UWB base stations.

If the base stations are fixed units that mechanically hold to the outlet, noting down with a reference image for easier finding where exactly they're plugged in lets one skip the GPS walk step for next year.