The Fernandes Sustainer is a magnetic driver designed to vibrate the strings of a guitar indefinitely, giving the effect of infinite sustain, or simulating amp feedback. This has been included on a number of Bellamy's guitars, and is most notably used during the slide intro for Invincible.
The magnetic driver is installed instead of the neck pickup on the guitar, and comes in two variants; the humbucker-sized FSK 101 and the single-coil-sized FSK-401. The two are almost identical in function, with two modes. There is a "normal" mode, that causes the root note to sustain, and a "harmonic" mode, that makes the string resonate at the fifth natural harmonic of the root note. The 401 also has a "mix" mode, that blends the other two modes, and an intensity control knob.