You could also set up other kinds of systems, but you would have to ensure they could not be foiled, like the key won't turn in the ignition without doing something inconvenient, like maybe checking the car seat and pressing a keypad?
On the other thread, there is a device that can be installed in police cars for their dogs which overheat faster than humans because of the way they breathe.
http://www.freerepublic.com/focus/f-news/1655013/posts?page=80#80
I can't get the link to code for some reason, have done it at least 100 times.
There should be a potential patent thread for FR. Ideas pitched by FReepers, worked out on threads, with resident engineers and patent lawyers filing on behalf of a non-profit that will eventually start reporting on FR on its disposition and activities.
Who knows, maybe FReepers could be selected by lottery to sit on the board for the non-profit corporation, and rotated every year. Assuming that it works out and patents are granted, and products are made and sold, etc.