Presence Detection using Bluetooth / RFID

You might ask this on the reelyActive site which is a special purpose built system for doing this sort of thing. See reelyActive Smart Spaces Revisited for how to integrate it with OH and some of the experiences and limitations with the system.

In general, the biggest problem with a smart phone is many of them spoof their MAC address so that you can see that and iPhone (for example) is present, but not a specific iPhone is present.