I had an SV650S that someone tried to steal. It was a dumb kid and not a professional as I could tell they tried to pop the ignition instead of just picking it up and trucking it off. I put a Scorpio i300s security system on it ($200 or so) and nobody ever touched it again. The Scorpio was just a basic siren alarm with tilt sensor (no perimeter sensors).

I traded the SV in for a GSX-R1000 and had it stolen after about 4 months. Thank God I had insurance on it, but I did not have gap insurance so it still cost me a few grand. I got the exact same bike again, but this time put a Phantom Tracking security system on it. Very pricey at $850 but it is GPS with 24 hour monitoring. They will call your cell phone if the bike moves unauthorized and call the cops if you don't answer your cell (and the bike is moving). That way there is a fail-safe so the bike is protected even if you are sleeping and don't hear the phone or whatever.

I have had the Phantom monitoring center call me numerous times... Once I parked in ClearWater beach and someone bumped it parking next to me. The monitoring center called me and told me it moved 6 inched off-center! I felt much better about leaving my bike out in the open after that... Of course they can also tell how fast you are going which bothered me at first, but they don't use it against you as I have gone well over 100 a bunch of times and never heard anything about it.