ImpactAlert
is a pedestrian-carried vehicle collision alert system  that detects
objects that are likely to
hit a pedestrian and alerts that pedestrian. The primary use cases are
visually impaired
pedestrians or pedestrians who need to be warned about vehicles or
other pedestrians
coming from unseen directions.  ImpactAlert makes use of a LiDAR
camera found on a commercial wireless phone,
processes the data over several frames to evaluate the time to impact
and speed of potential
threats. When ImpactAlert determines a threat meets the criteria set
by the user, it sends
signals through an output device to warn the pedestrian. Experiments
carried out in varied urban environments, ranging from densely crowded
to semi-urban in the United States, India and
China show that the system produces nearly no false negatives and few
false positives. The net result is an effective low cost system to
alert pedestrians in
an urban environment.