Antitheft systems are at best, a deterrent. If it's obvious to a thief that that jacking this truck won't be as easy as they like, your hope is that they'll move on to another vehicle. I have had some past experience with antitheft systems (no, not as in stealing cars), and here's some thoughts, "for what they're worth". Bear in mind, that my thoughts, and experience, is with older vehicles.
The obvious things. Don't leave loose valuables laying out in your truck. Anything- crackheads will steal a hot stove. Expensive stereo gear is tough. A high-end head unit can be camouflaged (if you're creative), but amps and speakers should be hidden, and not mounted out in the open as if they're on display. What tools and parts that you carry for roadside repairs should be stowed out of sight.
Locking up the truck has two approaches. On a beater with absolutely nothing to steal, not locking the doors can prevent damage by the criminally curious. Older Rangers are ridiculously easy to unlock if you know how, but modification can fix this. What can be done about "smash and grab" I'll cover below. I keep my trucks locked at all times, with nothing in view to be seen if the truck is cased, and all of mine have stock radios. None of mine have security systems; they definitely would, though, if my living circumstances put my vehicles in a higher risk situation.
I think that a "layered approach" is good.
Not being stupid is the first layer.
Don't advertise that you have something to steal. Park carefully whenever you can. Nice wheels, use security lug nuts. External accessories should be obviously difficult to remove- chain and lock (spare, winch), or security hardware (security Torx versus hex bolts).
A good basic remote-operated car alarm, well installed, is the second layer.
One of the biggest deterrents is an alarm's flashing LED dash light; it advertises that "something" is there, and is a deterrent against "smash and grab" (along with no valuables in sight). Car alarm systems can be "built up" to increase or enhance their effectiveness. I like the piezo sensor pickups that be installed in the doors, which detect attempts to jimmy the locks, or even trying the door handles in checking if the doors are locked. A GOOD shock sensor, properly installed, trips the alarm if the vehicle is struck.
A bonus, if you have power locks or add them, is gaining keyless entry with a remote-operated alarm system. A starter disable relay is also a basic common part of an alarm system; I would use that along with the following.
A safety net third layer would be an ignition kill through a hidden switch. There has already been some excellent suggestions on this by previous posters.
An ignition kill alone won't do much to prevent a smashed window and busted-up steering column, even if they ended up failing to drive it off. That's why I like the layered approach. Any effort made at theft deterrent, is only just that, a deterrent. You're just trying to make it very apparent on the front end that stealing YOUR truck is not going to be as easy as they'd like.
Hope it helps; good luck!
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