HOWTO build a Bluetooth "sniper rifle"

One of the security assumptions in Bluetooth is that attackers need to be quite close-by if they want to gain access to your phone or other device. Here's simple instructions for building a handsome, effective Bluetooth "sniper rifle" whose high-gain antenna will give you access to devices from miles away.
After a few seconds, John pointed the gun at the Library Tower / US Bank Building, which is the tallest building in Los Angeles. The building was .75 miles (a little over 1 km) from our position.

As more Bluetooth devices started appearing, John said, "This building is full of Bluetooth! Look we got some Blackberries!" He also explained that, with multiple guns, it would be possible to track a single Bluetooth device as the person walked around. In less than a few minutes, twenty devices were detected–all at distances over a half mile away! We decided to quickly conclude the scan, given police activity in the area earlier in the day from a bomb scare.

Link (via MAKE Blog)