What interaction system would you recommend for connecting two small devices?

Question

Do it yourself

There are small devices with a power source + a couple of LEDs, we are going to use them as electronic passes, ordinary visitors will have regular passes, security guards will have special ones. devices, if you touch the visitor's device with them, the green LED lights up, if you touch it again, the red LED is displayed again, what would you advise for this purpose? Can the intercom key tablet be programmed for this? Or are there other technologies for this purpose? No need to dissuade, we do it purely for ourselves, a hobby, so to speak

Answer 1

And why didn’t RFID suit classic for such purposes?