A simple Python script that will trigger an LED to light up when a known Bluetooth-capable device (such as your phone or fitness band) comes within sensing range.

detect_bluetooth.py

import bluetooth, time
import Adafruit_BBIO.GPIO as GPIO

search_time = 10
led_pin = "P8_7"
# You can hardcode the desired device ID here as a string to skip the discovery stage
addr = None

print("Welcome to the Bluetooth Detection Demo! \nMake sure your desired Bluetooth-capable device is turned on and discoverable.")

if addr == None:
    try:
        input("When you are ready to begin, press the Enter key to continue...")
    except SyntaxError:
        pass

    print("Searching for devices...")

    nearby_devices = bluetooth.discover_devices(duration=search_time, flush_cache=True, lookup_names=True)

    if len(nearby_devices) > 0:
        print("Found %d devices!" % len(nearby_devices))
    else:
        print("No devices found! Please check your Bluetooth device and restart the demo!")
        exit(0)

    i = 0 # Just an incrementer for labeling the list entries
    # Print out a list of all the discovered Bluetooth Devices
    for addr, name in nearby_devices:
        print("%s. %s - %s" % (i, addr, name))
        i =+ 1

    device_num = input("Please specify the number of the device you want to track: ")

    # extract out the useful info on the desired device for use later
    addr, name = nearby_devices[device_num][0], nearby_devices[device_num][1]

print("The script will now scan for the device %s." % (addr))
print("Feel free to move near and far away from the BeagleBone to see the state change on the LED.\nUse Ctrl+c to exit...")

GPIO.setup(led_pin, GPIO.OUT)
while True:
    # Try to gather information from the desired device.
    # We're using two different metrics (readable name and data services)
    # to reduce false negatives.
    state = bluetooth.lookup_name(addr, timeout=20)
    services = bluetooth.find_service(address=addr)
    # Flip the LED pin on or off depending on whether the device is nearby
    if state == None and services == []:
        print("No device detected in range...")
        GPIO.output(led_pin, GPIO.LOW)
    else:
        print("Device detected!")
        GPIO.output(led_pin, GPIO.HIGH)
    # Arbitrary wait time
    time.sleep(1)