A device locating method includes broadcasting by a first mobile device a signal comprising an identifier associated with the first mobile device. A second mobile device receives and measures the signal broadcast by the first mobile device to produce one or more signal measurements. The second mobile device transmits the identifier associated with the first mobile device and the one or more signal measurements to a computing system. The computing system receives the identifier associated with the first mobile device and the one or more signal measurements from the second mobile device. The computing system estimates a location of the first mobile device based on the one or more signal measurements, and the location is transmitted to a user associated with the first mobile device. A traffic flow determination method, product ordering method and associated systems are also provided.