In general, this disclosure describes location techniques for a mobile device. A mobile device may request permission from a server device to perform a ranging operation. Responsive to receiving an indication of allowance, the mobile device may output a first data packet via a radio signal, which is received by a beacon device that activates an ultrasonic transponder upon receipt of the first data packet. The mobile device then outputs a second data packet via an ultrasonic pulse. The beacon device receives the ultrasonic pulse and outputs a third data packet via a second radio signal that includes information identifying the beacon device. The mobile device calculates a time difference between outputting the ultrasonic pulse and receiving the second radio signal and determines its location based on the third data packet and the time difference.