A professionally installed and certificated Datatool will always be the best Alarm/ immobilizer you can buy. It will also be a genuine asset when it comes to insurance time. (saves me £90 a year so it's on it's way to paying for it's self.)
My Datatool system 3 is brilliant at being an alarm, just make sure you ALWAYS put it in service mode before you do any work on the bike and if you have intervals of more than 2 weeks of riding you will definitely want a battery conditioner.
I hope this helps
