This paper by ZigBee Alliance explains how ZigBee and other unlicensed wireless technologies can co-exist without interference. ZigBee operates in 2.4-GHz band worldwide, in the 900-MHz band in North America and Australia, and in the 800-MHz band in Europe. Possible interference sources are WiFi, Bluetooth, portable telephones and microphones, WiMax, and microwave ovens. ZigBee avoids interfering by employing a frequency division multiple access (FDMA) communications protocol. Methods to avoid message collisions and to achieve successful reception are described. The benefit of a ZigBee mesh network is explained. Various tests supporting and criticizing ZigBee performance are presented.