Wireless Communication with XBee Radios - Exploring Arduino: Tools and Techniques for Engineering Wizardry - page 253

■ There are a variety of options for powering your Arduino that do not
require you to stay connected to your computer via USB.
■ You can communicate wirelessly between your computer and an Arduino
using XBees.
■ You can communicate wirelessly between two Arduinos using XBees.
■ The millis() function can be used with state variables to create “non-
blocking” code that implements time delays.