The flexatone is a modern percussion instrument (an indirectly struck idiophone) consisting of a small flexible metal sheet suspended in a wire frame ending in a handle. 
History, construction and technique
An invention for a flexatone occurs in the British Patent Records of 1922 and 1923. In 1924 the 'Flex-a-tone' was patented in the USA by the Playatone Company of New York.
Wooden knobs mounted on strips of spring steel lie on each side of the metal sheet. The player holds the flexatone in one hand with the palm around the wire frame and the thumb on the free end of the spring steel. The player then shakes the instrument with a trembling movement which causes the beaters to strike the sides of the metal sheet. While shaking the handle, the musician makes a high- or low-pitched sound depending on the curve given to the blade by the pressure from his thumb. A vibrato is thus produced.
An alternate technique involves removing the two wooden knobs and their mounting springs, and then using a small metal rod (e.g., a triangle beater) held in the free hand striking the strip of spring steel. The pitch is altered in the same manner as the previous technique. This method of playing results in a different, more constrained sound.
The flexatone is sometimes heard in funk music, and occasionally in pop music for special effect. It is occasionally used in the soundtracks of films or cartoons to represent "ghosts" or other paranormal phenomena.
The instrument is rarely used in classical music; Arnold Schoenberg employed it in his Variations for Orchestra and his unfinished opera Moses und Aron, and Aram Khachaturian wrote for it in his Piano Concerto (though here the flexatone is now often omitted). It is also used in Jonny spielt auf by Ernst Krenek, Erwin Schulhoff's Symphony No. 1, and John Corigliano's "Symphony No. 1". The cellist in Sofia Gubaidulina's The Canticle of the Sun plays a flexatone in the middle of the piece. Dmitri Shostakovich also uses a flexatone prominently in his opera The Nose, to characterise the nihilistic schoolteacher in Lady Macbeth of Mtsensk, and in his rarely performed suite Hypothetically Murdered. Alfred Schnittke used it in the death tango movement of his Faust Cantata as well as in the Tuba Mirum movement of his Requiem and in his Viola Concerto. In Schnittke's score for the ballet Peer Gynt, the flexatone represents the sound of the moaning wind. György Ligeti used it in many of his works, such as the second movement of his concerto for piano and his opera Le Grand Macabre. Peter Maxwell-Davies uses it in the third movement of his Symphony No. 1, as well as three of them at the climax of his opera The Lighthouse. Brian Ferneyhough calls for it in his 2011 orchestral piece Plötzlichkeit. The 1964 ballet The Display, by Australian composer Malcolm Williamson, also includes a part for the flexatone.