On 17 May 1904, near Cologne, Christian Hülsmeyer demonstrates his Telemobiloskop: a spark-gap transmitter, simple parabolic antennas, a detector, and an indicator, designed to ring a bell when a vessel passed near the system, at a range of several hundred meters. It is the world's first operable device capable of detecting radio wave reflections, a direct predecessor of radar. He patents the device in Germany, the United Kingdom, and the USA.