Measure distance between 2 devices

Hi there, I’m a freshman at a university of technology and i have absolutely no idea what i am doing (: I’m trying to find out if there’s any way we can measure the distance between 2 devices. We only need to know if its far, near-ish or super close. We’ve looked into bluetooth, RSSI and XBee, but than again we have no clue. Please help us (:

duplicate post:

https://forum.sparkfun.com/viewtopic.php?f=13&t=36679