Actually, the chips are essentially the same. There are passive and active RFID tags. The tag is the combination of the chip, an antenna, and in the case of an active tag, a battery.
Active tags are not used in retail, and not used to to tag individual products. They are too large and too expensive. They are typically used to tag a pallet of goods.
A typical active RFID tag is a plastic weatherproof enclosure, rectangular, about 8" by 2" by 2". Some connect to an external antenna, making the contraption even larger. Smaller active RFID tags are available, but they do not target retail applications.
From SmartCode Corp, a supplier of RFID products:
"Active tags have a life of about ten years, due to their batteries. Still, active tags are an interesting option that allows higher data transmission rates and greater distances between tag and reader. They also offer better performance in electro magnetically noisy environments."
"The main usages for Active Tags:"
"Transport and distribution"
"Factory automation"
"Rail industry"
"Asset tracking"
"Industrial applications"
Active tags are what are being tested with WiFi and middleware scanning system for live tracking.
About VeriChip - "The First RFID Company for People" VeriChip is a subsidiary of Applied Digital and the only company to provide both implantable and wearable RFID identification and security solutions for people, their assets, and their environments. From the world's first and only FDA-cleared, human-implantable RFID microchip to the only patented active RFID tag with skin-sensing capabilities, VeriChip leads the way in next-generation RFID technologies. Today, over 4,000 installations worldwide in healthcare, security, industrial, and government markets benefit from both the protection and efficiencies provided by VeriChip systems. For more information on VeriChip, please visit www.verichipcorp.com.