Any mechanism that could switch the magnet on and off would require energy. E.g. you could put a magnet next to it with opposite poles, which would mostly cance

Any mechanism that could switch the magnet on and off would require energy. E.g. you could put a magnet next to it with opposite poles, which would mostly cancel out the magnetic field, but would require a lot of force to push them together, which is work, and thus requires energy.