There are distance-bounding protocols[0], but I don't think anyone has implemented them in something as small as a car key yet.
[0] https://en.m.wikipedia.org/wiki/Distance-bounding_protocol
[0] https://en.m.wikipedia.org/wiki/Distance-bounding_protocol
It's only a matter of time till NFC credit cards get read with a high power reader and proxied across a cell connection to steal money from someone hundreds of miles away from the thief.