It's an E-Bow. It was first made in 1969 to simulate sounds not normally played on guitar by controlled magnetic pulses revolving around 1 string which creates an infinitely lasting sustaining effect if controlled correctly. The E-Bow plus also has a second mode adding more harmonic overtones to the note, which i did not need to use, as most of work here was actually the guitar tone itself, but the E-Bows sustaining effect helped.