I second the Ravelco system. No moving parts to go bad on an extended journey, and virtually impossible to thwart without hours of work. It won't prevent the contents of the vehicle being stolen, but short of running into a thief with a tow truck, you know your vehicle will be there when you come back.
I installed a Revelco system in my 05 Sierra 2500 HD duramax.
Prior to install, I toned all the wires using a meter, then drew up a schematic incase I ever lost the cap while out of town. I then made two jumper wires that allows the system to get me on my way. The scematic is writin in code and stashed away and the two jumpers are inbedded within the harness.
I can only imagine the PITA to get the rig started if one was to loose the "KEY".
