The passenger seats of certain cars use electric field sensing in the seatback to determine if there is an adult passenger present, to decide whether to enable the passenger-side airbag. (Though simply sensing by weight is also common.)
For an example of an electric field sensor, check out the Motorola MC33794.
https://medschool.mc.vanderbilt.edu/biosci/bio_fac.php?id3=9...
What a brilliant read!