Don you have a good article discussing how this communication from car to key fob works?

Every fob like this that I’ve seen isn’t effective unless the key is close to the car (inches), because it uses a no-power system in the key fob, similar to a card reader (so no battery required in the fob to unlock car and start engine, once in close proximity). I’ve tested this on a few cars by removing the battery in the key fob.

Other functions (door locks, remote start etc), seem to be provided by conventional key fob electronics.

I’m sure there are several different ways this is accomplished, so any insight would be useful.

Thanks!