I found this research very interesting, its about a method to  
synchronize (pairring) two devices using bluetooth,   
through a synchronous shake pattern using the accelerometer.

As related in the article its a new way to improve the security in bluetooth connections.

a demo video can be seen in:



more information is avaliable at:

http://technology.newscientist.com/article/dn12912
http://eis.comp.lancs.ac.uk/fileadmin/eis/publication/2007-ShakeImp.pdf