It's worth mentioning that the Lumia 620 has been gifted with the same distortion-free, high-amplitude mics embeddedinside the Lumia 920 -- more on that in the camera section.
Embeddedinside it is a batteryless RF switch, and the way it works is that upon the release of the spring mechanism inside, a tiny bit of power is generated for the 2.4GHz RF transmission ( ZigBee compatible), and whatever device is connected to the RF control outlet on the other end will receive the on or off signal.