The most sensitive photo slaves available, range up to 3000 feet! Works indoors or out: ambient light filter prevents interference from bright sunlight or false-triggering from flickering fluorescents. 360° reception, works around corners and behind obstacles! Available with either "H"-prong or monoplug sync connector for direct connection to virtually any professional flash or power pack. All Ultra Slaves feature standard PC terminal as alternative sync connector. Lower-sensitivity XL Model (range up to 600 feet) also available.