An alternative to RFID for supply chain management is a wireless personal area network or WPAN, consisting of devices that communicate with each other instead of with a reader. The word “personal” in the title does not mean that there is always a human user, instead it refers to the limited range of the wireless communications: approximately 1 meter from one device to another. WPANs are of various types and here we focus on the low power version that is standardized by IEEE (2003), and is being commercialized by the industry consortium, the Zigbee Alliance, which has developed a specification for wireless personal area network applications (Zigbee, 2006). WPANs require each device to be powered, typically with a battery, but they transmit low data rates at low power so that battery life can exceed a year.