He could have run a wire up through the house walls to an LED indicator but decided to go wireless with a 433mhz transmitter. There is a second Arduino inside equipped with a 433mhz receiver.

Together with the Arduino code you will require as well as schematic’s and part lists allow you to create your very own one-handed Arduino powered quad copter transmitter.

Long-range RC transmitter “I started using Bluetooth devices like the HC-05 modules, but I found that these sometimes randomly disconnected.