A warning device in one embodiment includes a housing which is portable, the housing containing preferably a microwave transceiver operating as a proximity-sensing device, a stroboscopic lamp and/or a horn disposed in the housing in electrical connection with the sensing device for emitting a series of flashes and/or honks in response to the sensing of an object within predetermined range of the sensing device, a battery in the housing for powering the sensing device and the lamp and/or horn, and a system for mounting the housing to a variety of supporting objects.