Bluedriving?

I'm interested, not as someone who does this sort of thing, but as someone who has to protect against it. My quesiton is: if you modify an interface so that it can pick up communications from a mile away, how do you tell which is what and where?

Also, does anyone make directional antennas for Bluetooth? Or is it even worth the trouble of performing periodic scans because even cell phones have an interface nowadays?

Thanks to Furrygoat for pointing out the site.