How to activate car mode with a magnet? The Google Nexus 7 tablet has lots of reed relays and magnets.

Some toggle the screen, others activate the wireless charging dock. I suppose there is a position for activating car mode (never putting screen to sleep). I'd like to put a magnet (or several if necessary) into my car dock, so I can trigger car mode, whenever I put the tablet in there.

Unfortunatelly, I couldn't find a page, that will describe the various positions of the reed relays inside the device.
the best way is NFC Trigger.. there is an app (nfc trigger) that can activate car mode automatically when the tag is close to the tablet