Recently I came home with a broken spoke on my rear Campy Eurus wheel.
Previously I had identified a spoke with a slight bend near the rim,
where I'm reasonably certain the previous owner had attached a magnet.
Upon inspection the spoke with the bend was indeed the broken one and
it hadn't simply broken, but the kinked section was entirely gone, so
about 1/4 inch of the spoke was air.

The Spokesman, in Santa Cruz, serviced the wheel for me and I opted to
buy the entire mini-kit, as they hadn't any spare spokes for these
wheels in stock. There being 3 different spokes among a set of wheels.

These spokes are few in number (16 front, 21 rear) and comparatively
less material, cross sectional, than most spokes and thus must be
manufactured from a very strong (and typically more brittle) alloy.
Slight imperfections where the material elasticity and strength are so
critical aren't something to encourage by screwing a cheap magnet to
spoke and bending or scratching it.

I've since picked up a magnet which clamps the spoke between plastic
surfaces.