Like treebilly notes, chaps work by cutters snagging a hard-t0-break fiber, dragging it into the sprocket, and stalling out the saw. Most have a warning on the label stating that they are not effective with electric chainsaws due to their 'constant torque'. We did a 'test'/demo at a GTG last year with some outdated chaps and a 40V battery operated chainsaw. That saw has an overload protection circuit and 'stalled out' when the fibers got tangled in the nose sprocket of the bar.
I don't know if they might provide some protection in certain circumstances, like with the nose sprocket on the battery saw. I usually wear them anyway as a force of habit.
Philbert