In general my Idea was to use a BT Master Module (Tried with EGBT-045MS (as i assumed)..)

I thought it would report identificable BT Devices. Somehow it nearly doesn't respond anymore if i set it to Mastermode and Inquire.

After Getting the BT ID, i would check if the RSSI is over a certain threshold and enable a Button to unlock the door... But first i have to find an other BT Master module or get it running ...