Harvey, it'll show you the distance upside down. You'll need to use a phased transflux inducer to invert the signal 360° As for the car battery, make sure you install a high capacity fuse between the two posts and install a choke in series with a 555 timer attached to that resistor.
And on my own ranging ideas, anyone have a (preferred) parts supplier suggestion for an inexpensive ~10cm - ~10m and a ~1m - ~50m ranging circuit module? I'd like to put 1-wire solutions in at the fore/aft of my vehicle to serve different purposes.
I.e. parking for the first, possible collision alert for the 2nd (fast delta).