Electro-acoustic guitars, including electro-acoustic classical guitars, often come fitted with piezo pickups. These 'contact' pickups aren't actually magnetic, but use crystals that generate an electrical charge - in other words, the crystals respond to the resonance of the instrument to result in a more natural sound that better retains the acoustic character of the kind of wood used to build it. Since the strings are made of metal, you can also amplify a steel-string acoustic guitar with a magnetic pickup, like a soundhole pickup. These pickups can be built-in or you can get versions that can be clipped onto the soundhole so you can plug your acoustic guitar straight into an acoustic amplifier, a PA system, or recording equipment.
