Ekahau’s T301W Wi-Fi Bracelet will tell you exactly where the person is who is wearing it. And it doesn’t use GPS. Instead it uses Wi-Fi. But the T301W only works on preconfigured Wi-Fi networks that are coupled with additional beacons. Basically you build your own Wi-Fi triangulation network in a small area.
That may not be the best option for you, but it’s a neat idea. For $60 you get a waterproof wristband that operates up to a month between recharges. Hospitals can track patients, family members can locate one another at an amusement park etc.