This study developed a low-cost Proximity Warning System (PWS) that can be used to prevent collisions in underground mines or road tunnels. The PWS receives signals from Bluetooth beacons attached to mine workers and equipment via smartphones mounted in vehicles and provides the drivers with a primary (caution) alert and a secondary (warning) alert in stages according to the intensity of the signal. After identifying suitable RSSI threshold values for the caution and warning zones based on the results of a preliminary experiment, a field test was conducted in an underground tunnel. From the results of 50 experiment repetitions, the accuracies of the first and second alert occurrences in the caution zone and warning zone were found to be 93% and 95%, respectively. The Bluetooth beacon–based PWS can be used effectively in mine safety management because it is relatively inexpensive, its functions can be easily extended using the smartphone application.