On this wikipedia page linked in by GopherT:
https://en.wikipedia.org/wiki/Smart_key#Outlook

On section Outlook:

<some original text removed here>
Here are some general trends of the advance (AD) and series development (SD):
<some original text removed here>

• AD: using electric field antennas instead of magnetic field antennas (cost reduction)

It says the new one use electric field, and the old ones (say 5-10 year back?) use magnetic field. So what is that 125kHz signal? Is that rf? or magnetic field? or are they interchangeable in this?

 

Just a little more info for whoever interested:

according to this app note: http://ww1.microchip.com/downloads/en/devicedoc/51115f.pdf, page 9.



At low frequency, it doesn't have orientation problem. So AnalogKid was right. And I believe I was confused this inductive proximity sensing with low frequency RF (125khz). That lead me to search for an answer that doesn't exit.

I am convinced that those smart key, they use two different frequency. 125khz one for proximity sensing, and 433/303MHz for remote control.

Thank you for all the replies, patience and your toleration for my stubborn.

Thanks guys!

 

you: That lead me to think they are using inductive proximity sensing.

me: Nope. It is plain old RF. The key fob does not radiate anything most of the time. It sits as a very low power receiver waiting for the proper wake up code. Then it transmits back its own code. At high frequencies inductive loops have all of the orientation problems you have pointed out. Radio has none of these.

ak