433 Mhz Remote Control Transmitter-Receiver pair
NOTE: These are labelled "433 Mhz Data Transmitter and Receiver" by the manufacturer, but mainly transmit and receive 4 on-off channels for remote control purposes.
NOTE: The transmitter usually comes with an attached antenna wire of about 25 cm. The receiver often does not have it's wire antenna soldered in place, so that other antennae may be used.
The easy way to use these is to plug them in to a Sensor Shield with 3-wire cables (Usually supplied with the transmitter and receiver). The cables them supply +5V, Gnd, and (S)ignal.
The Transmitter connects to Arduino pins you set as Output, and control which of the 4 channels you send. The Receiver connects to Arduino pins you use as Input, and will become active when a channel is received.
So basically you have 4 independent bits that can be transmitted from one Arduino to another. Or you can power the receiver separately and use the digital outputs to control some other device.
(Working on a test Software Sketch)