Ah it's an ideal way of protecting the 'van', physical with the cable that has to be removed to take the van away is the first deterrent.If obvious it will be a deterent to a criminal and will set the alarm if tampered with.The cable connection gives a level of security in its self.
Any wireless system, think about it, you've gone shopping for the day, 'van' on drive, hitched up and removed with the wireless system, making a noise? in the house, 'van' goes down the road.