After this happened:
http://forums.sv650.org/viewtopic.php?t=38639
I can totally rate the Xena XM9 alarmed disk lock. It only goes off with a reasonable amount of movement and I havn't had any trouble with moisture. Batts last about 6 months maybe a bit less but I found cheap ones on the internet. It saved my bike and it was on the other side of the road and I was asleep in my flat on the 2nd floor! I think my brain is tuned in to the sound of it! Obviously the down side of any disk lock is that if you forget about it or someone tries to steal the bike, you get a warped disk. I know. But I've been told you can get 'em straightened for £30 a pair so I think it's worth it. You tend not to ride off with it on the disk as it is beeping like crazy by the time you have the engine started if you forget to take it off...
