I just (like, 15 minutes ago) picked a used one up at a charity shop. It's a lock with an alarm function, which is supposed to go off when you mess with the cable or even move the bike. I'm a bit sceptical, as it has a round key like the Kryptonite U-locks, but it was dirt cheap so I thought why not. It might have an intimidating effect at least.

Does anyone else use this, or a similar lock? And how safe do you think it is?

http://www.ericas.se/q/cycle.jpg

Oh, sorry, this should probably be in the 'General Cycling' forum.. I just realised 'Advocacy and Safety' is about one's own safety, whereas I'm more concerned about my bike's. :D