Note: something with the same purpose but a different way of doing it can be found here.
This is a theoretical ‘invention’ that is a good future project for me. I’d like to give you the following scenario: you have a base-trim car that does not have the fancy audio controls on the steering wheel. In order to have them, the higher trim levels have the extra buttons that are wired back to the stereo (or other systems). More controls = more wires. I think it would be pretty cool to add a RFID reader ‘behind the scenes’ that controls a relay board which shorts out (‘presses’) the internal button terminals in the stereo. For the controls, small flat buttons like most microwaves have can be used that comprise a chip and an antenna connected with a miniature switch. The reader is ‘listening’ non-stop but not capturing anything because the tags are inactive (no antenna). When the button is pressed and the RFID chip is finally reunited with its antenna, the reader tells our controller to do what we want it – control a relay, etc. That would be a neat way to create a true remote button that does not require a battery or wiring!