Detect and measure iPhone’s BLE RSSI level: Which one to use? XIAO nRF52840 or XIAO ESP32-C3?

I’d like to create a simple doorlock which at the touch of the button unlocks a door if a person with one of several previously specified iPhones in his or hers pocket is standing close to the door (the working limit should be let’s say 3 meters).

My idea is to measure the RSSI level, although I’m not sure if that the signal is a) equally strong across various iPhones (same models, let’s assume) at the same distance and b) whether the RSSI levels resolution is defined enough to distinguish whether someone is less than 3 or actually 15 meters away.

Furthermore it needs to work reliably everytime and without the iPhone’s Bluetooth fully connecting to the XIAO board first (in a sense that it says „Connected“ in iPhone’s BT settings).

So the big questions are:

  1. Is this feasible with the BLE signal the iPhone’s sending out, just by the XIAO board scanning for it?
  2. Which board would you recommend? XIAO nRF52840 or XIAO ESP32-C3? (Low power consumption and reliable BLE comms requested).


One of the questions partially answered: According to YouTuber Andreas Spiess the nRF52840 is way more power efficient when used as a beacon, than the ESP32-C3. Does that also apply when the nRF52840 is the BLE receiver? (Sorry if this might be a stupid question, not an expert).