Recommended · for beginners
Arduino Tutorial #12: Wireless Communication
Why people recommend it
A tutorial on pairing 433 MHz transmitter and receiver modules with an Arduino Uno, linked as a starting point for simple wireless projects.
Watch for: Uses an Uno; swap in a smaller board for compact builds
In their words
HumanHarddrive on youtube got a tutorial on the DX transmitter and receiver.
LoneWolf on arduino.stackexchange.com, Jun 2014. CC BY-SA.