With that caveat, to answer your question, you'd probably use Bluetooth LE devices that everyone carries. If everyone had wi-fi devices, you could use wi-fi triangulation software. This is usually an add-on package to existing enterprise wireless solution.

You could also do active NFC tags and have choke-points with scanners everywhere.

I have my own Python script at work, appropriately named creep.py, that locates people by wi-fi by logging into our enterprise wireless system, checking what AP their MAC/DHCP client ID/username combo is connected to, gets the RSSI, then runs that through some if/else statements to determine what room they're in to a high degree of accuracy. The script also gets readings off the adjacent APs, as well, for better triangulation. I keep quiet about this script, lest it be used for police state purposes.

The above is a simplification of the script, but if RSSI is approx <=55 or so, then the person is likely in the same room as the WAP, given normal US construction practices. ~65 or so, there's probably a drywall wall between the person and WAP, etc etc. This is an extreme oversimplification, but gives you an idea.

tl;dr:

Your tracking options are:

- Bluetooth LE

- Wi-Fi

- NFC

- GPS devices

None of these will get you to a couple inches of accuracy. Think more like "room-level accuracy".