The
magnetic detector or
Marconi magnetic detector, sometimes called the "Maggie", was an early
radio wave detector used in some of the first radio receivers to receive
Morse code messages during the
wireless telegraphy era around the turn of the 20th century. Developed in 1902 by radio pioneer
Guglielmo Marconi from a method invented in 1895 by New Zealand physicist
Ernest Rutherford it was used in Marconi wireless stations until around 1912, when it was superseded by
vacuum tubes. It was widely used on ships because of its reliability and insensitivity to vibration.