Key proximity detection?

I just noticed today that when I walked by my locked car today with my key (standard key - old school - not keyless fob) in my pocket, a mechanical sound and click came from the car. I also think i notice the key icon come on in the cockpit before I put in the ignition. Just curious what was happening - does it disable the alarm as I approach ? I didn't realize these older style keys had 'infrared/radio freq technology.

I had that happened to me when I had my 04 645. Even before I put the key into the ignition, the systen would detect that the key is close. I am thinking that the key may have the technology in it for convience features but to make it work all the dealer would have to do is install the module in the car to make the feature active and not necessarly change out the key. The convenience feature is an option.

most keys now have a chip inside that is detected by the car before it allows the ignition to start... I suppose they are using that same technology