Comment proximity triggered actions (Score 2) 101
Just have a look at
http://sourceforge.net/projects/blueproximity/ (mac),
http://www.daveamenta.com/products/btproximity/ (windows),
http://blueproximity.sourceforge.net/ (linux).
This will detect you when you walk by with your bluetooth device.
You can trigger actions as desired when in range - http://hints.macworld.com/article.php?story=20091221173111783 .
There is even a commercial alternative - http://themha.com/airlock/ .