Abstract: A warning device includes a housing, a power source, a control unit, sensors and alarms. The control unit is in the housing. The sensors are operably connected to the control unit. The sensors detect the presence of an object in each of at least two designated detection zones. The alarms are operably connected to the control unit. The alarms are responsive to a signal from the control unit when objects have been detected in at least two designated detection zones. A method of warning of potential collisions including the steps of: defining at least two designated detection zones; detecting the presence of an object in the zones; determining when objects are present in more than one zone and determining if these are in defined potential collision combinations; and if the objects are present in the more than one zones and in the defined potential collision combinations then activating a warning.