In the real world, you aren't going to track them down to a couple inches accuracy. There's too much variance in physical materials and positioning, let alone the RF environment.
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".
