1. A computer-implemented system for identifying obstacles in path of a pedestrian using a handheld computing device, comprising: a motion estimator configured to receive an input from an accelerometer residing in the handheld computing device and operates to determine speed at which the handheld computing device is moving; an acoustic detector interfaced with a speaker in the handheld computing device and operates to emit acoustic signals via the speaker, the acoustic detector interfaced with a microphone in the handheld computing device and, via the microphone, operates to detect the acoustic signals reflected by objects proximate to the handheld computing device and, in response to the detected acoustic signals, determines distance to a given object using timing between the emitted acoustic signals and the detected acoustic signals; and a motion filter interfaced with the motion estimator and the acoustic detector, the motion filter determines rate at which distance to the given object is changing from the distance measures received from the acoustic detector and, in response to a determination that the rate at which the distance to the given object changes is substantially same to the speed at which the handheld computing device is moving, identifies the given object as an obstacle in the path of the pedestrian, wherein the motion estimator, the acoustic detector and motion filter reside in the handheld computing device and are implemented by instructions executed by a processor residing in the handheld computing device.