Abstract: A vehicle detection and collision alerting device and method is described. The vehicle detection device is used by a user to detect an approaching vehicle. The vehicle detection device may include a housing and a mount attached to the housing for securing the housing to the user or the users equipment. An optical sensor secured to the housing, facing generally outward. A processor is in communication with the optical sensor to receive data and execute an algorithm to analyze the received data. This algorithm is configured to determine the size and distance of the approaching vehicle and also calculate its velocity and trajectory. Alerting modules to alert the user and to alert the approaching vehicle are configured to receive signals from the processor when a potential collision is identified based on the data being processed.