Magnetic acoustic guitar pickups employ a coil which senses the magnetic vibrations of the strings, and translates them into sound. They are typically “clipped on” to the edges of the sound hole under the strings.
Can you put pickups in an acoustic guitar?
Acoustic guitars can be tricky to amplify. Many modern instruments are equipped with onboard pickup/preamp systems, so the job is practically done for us. But for acoustic guitars that don't already have onboard electronics, many different pickups are easily available and affordable.