I use a ABUS GRANIT Detecto X Plus 8077 = http://www.abus.com/eng/Mobile-Secur...to-X-Plus-8077

Not exactly cheap (EUR 250 + chain), but the 3D motion detection system is really worth. Once activated, if you change the lock position for more than a couple of degrees, it will wake up the entire neighborhood.

In conjunction with the very bored and biker friendly old lady that has her window right next to my bike...