How to find out that 2 devices are nearby (~ 5 meters)?

Question

Electronics

Hello! It is necessary to determine that 2 devices are nearby (~ 5 meters). NFC is not suitable - too small range. I thought to use Bluetooth LE, but there is insufficient accuracy + using bluetooth is an overhead, I need one device to transmit a code to another, no more.
I thought about using RFID tags, but readers cost a lot of money.
Is there any way to do this? Without a huge overhead like Blutooth?

Answer 1

if there is no need to define "through the walls", then you can get by with a simple infrared LED like on a TV remote control, it will consume anything less than bluetooth, the accuracy will be a little doubtful of course, but it depends on why it is needed at all

Answer 2

"radio call" and the like, adjust the transmitter power to taste.