alt Hacker NewsThe one that uses a semi-permanent magnet for that mechanism? It's the only use I'm aware of a switchable permanent magnet (alnico and rare earth half-cylinders wrapped in a coil; pulsing the coil switches the alnico to be either parallel or anti-parallel with the neodymium, turning the whole assembly on or off) in a commercial product; I bought it just for that.
They have multiple that can do this.
It sounds like you are talking about the style in the MX Master, which is electromagnetic and controlled via software.
They also have a physical version in the M720. I do not know how the mechanism works, but it is controlled by a mechanical switch on the mouse.