How does a Philips Hue Tap transmit a radio signal without a battery?

The Philips Hue Tap is a remote control for a Philips Hue lighting system. The buttons can be configured to trigger some action on the Hue bridge, such as turning lights on in a particular room.

The interesting thing about the product is that seems that the energy from pressing the button is enough to transmit a radio message to the Hue bridge.

The Philips Hue tap is powered by kinetic energy, which means that when you press the light switch you generate sufficient energy to control your smart lights. A truly wireless, batteryless, solution.

How does this work? About how much electrical power is generated by pressing the button? What components would be needed to make something similar?