For snatch and grab there is none. By the time they gain access, normally within seconds they can have what they want in a matter of a minute. Alarms don't work because nobody pays attention to them anymore. Think about it, when was the last time you were in a parking lot and heard an alarm going off and even had a remote thought that someone might be stealing something? Your best medicine is to keep anything valuable bolted down or not in the vehicle to begin with. BTW, recent trends, the number 1 & 2 items stolen in snatch and grabs are your registeration and your garage door remote. They got your address and they got access. Keep the registration in your wallet.
As for flatout theft, my only advice is get something with a tracking device because truth be told, if they want it, they will get it. All you can do is hope you notice it quickly and they haven't had the time to find the tracker. In Colorado and California the big thing now is they just pull up to your rig with a tow truck with a magnetic repo buisness logo on it, hook up, and haul it away. Nobody even bothers to question it when they think that it's an official repo.
Lastly, keep really good receipts of all mods and make sure your insurance company is aware of them and will cover them, mine does ( State Farm). Once it's stolen it's extremely rare that it's recovered. Normally they have it stripped within an hour and sell the parts on such sites like ebay.