The iButton seems like the trick. What's the range on the readers, though (and the power consumption)? Would having an iButton on your key ring (in the ignition) be close enough to activate through a sensor in the display module?


The power consumption is very low. But the range is basically zero - iButton works on the Dallas 1-wire specs (1 wire + ground, multiple device serial), and requires the button to be 'touched' to a reader clip. Actually, you could program the empeg so that the crypto button was only needed after constant 12V had failed, similar to how most OEM stereo code-locks work nowadays, (only much stronger than a 4 digit pin obviously).