Let me know if you got it to work - this is just a little Bash script to do the work, basically this is what it does:

1. execute hcitool command to get a list of all devices
2. use the awk to filter out the lines with 'BD Address' in it
3. use grep to see if we have a match
4. use dbus-send to display an alert if there is a match

Cheers, Arne