(This idea has recently been edited for violence. As much I'd love to see the Karmic justice of a carjacker being crushed by the car he's trying to jack, I do realize that that may be considered by some folks to be cruel and unusual punishment, and needlessly violent, and I'm more than willing to make
a concession in the name of peace, which ideas such as this are supposed to promote.)
I remember reading somewhere that in a lot of rough towns with high rates of violent crime, it's a common tactic for a stalker/carjacker/mugger to crawl under an empty vehicle and lie in wait until the owner approaches the vehicle, then slash the owner's legs with a knife as they're getting into the vehicle and drag them out, where they do whatever is they plan to do to the hapless victim. This idea is intended to counter such tactics.
Ok, the idea is for a set of underbody lights to be mounted... well, on the underbody. When you approach your vehicle, before unlocking the door, you press a button on the fob to activate the lights, revealing anybody who might be lying in wait. Upon spotting a baddie under your car, from a safe distance, you press another button. This button causes panels to drop down around the bottom of the car, around the perimeter, which box the baddie in and prevent his/her escape. The panels look like steps, such as those found on trucks, Jeeps, and SUVs, which simply fold down to touch the ground, where they lock in place. On cars, if you don't want steps, then they can be folded up to fit snugly against the doors, where they pull double duty as side bumpers.
Once the assailant is safely and securely trapped, you simply go back inside and call the police. When the police arrive, they have their own fob that re-raises the drop panels to release the criminal into their custody. A little sticker in the window with a warning on it should suffice to prevent lawsuits resulting from any injuries caused by extremities being caught (and possibly severed) by the panels. And if the carjacker happens to bleed out before the police can arrive and provide medical assistance, then the world is no worse off for his/her loss.
Also, if the carjackers get wise to this and decide to place wood blocks under the vehicle alongside them to prevent being pinned, and disable the lights, you can spot the blocks pretty easily from a distance and just go back inside and call for an officer to check it out.
An alternative use for this device, rather than trapping carjackers, would be to simply have the drop panels always down when the vehicle is parked. This would serve multiple purposes. First, it would keep pesky stray animals out from under your vehicle. Here in Spokane, we have a problem with marmots climbing under vehicles and chewing on lines, wreaking all sorts of havoc. Second, it would keep would-be carjackers from getting in there in the first place. Third, for those of us with vindictive ex'es, it would make it nigh impossible for a saboteur to access your brake lines (I've had that happen) or rig a car bomb to your ignition. Unless, of course, they simply use a slimjim to open the doors. But that's a problem for another Baker to solve.
Note: For those of you who will undoubtedly raise objections based on the increased hazard to the owner of performing maintenance or repairs under your vehicle, I'd like to remind you all that you're never supposed to go under a vehicle without jackstands in place anyway, as it says on a warning sticker that comes on most floor jacks. You'd just have to make sure to observe that rule more frequently than you currently might.
And for those who will raise concerns about children playing under vehicles, I'd like to point out that a kid has absolutely no excuse for playing under vehicles at night, and if he does in that kind of neighborhood, he deserves what he gets. Especially given that young teenagers are often the most violent criminals in many neighborhoods, trying to earn the respect of their fellow gang members, and a vehicle owner in such a neighborhood cannot be expected to simply trust that youth = innocence.