I have a lockpick sitting in my office waiting to be installed, it does a lot more than just let you use the Nav too, it also allows for DVD's picture (not just audio) to be seen while driving and other things like access the reverse camera at all times (so you can see behind you even when driving forward for instance)
Regarding how it works, i read somewhere it uses several things, like GPS speed/ping and transmission gear (it detects your in P or D for instance)