One of the most popular and well-documented ways of connecting to Arduino via an RF connection is to use an XBee device. This device uses a technology called ZigBee, and it is made for long-range wireless communications. These types of devices can work up to a range of 1 mile.

The ZigBee standard is built upon the IEEE 802.15.4 standard, a standard that was created to allow a set of devices to communicate with each other to enable low data rate coordination of multiple devices.

The other standard that you might hear as you try to purchase or use devices like these is XBee. This is a specific company's implementation, Digi, of several different wireless standards with standard hardware modules that can connect in many different ways to different embedded systems. They make several devices that support ZigBee standard. The following image shows the type of device that supports ZigBee attached to a small XBee-specific shield that provides a USB port:

The...