Feel like you're being followed? Maybe it's a tracking tag on your jeans or one implanted in a credit card. The tags are called radio frequency identification or RFIDs, and every day they are becoming more and more a part of our lifestyle. These Orwellian microchips, as minute as a grain of sand, identify and track products and even lost children at theme parks. They're being implanted in humans to alert hospitals about medical conditions. The tags can be so tiny, you may never know they are there. Retailers claim RFIDs are essential: alerting them when they're low on lipstick, air filters, sodas and other inventory. Embedded tags aren't so obvious. Hitachi Europe recently developed the world's tiniest RFID integrated circuit, small enough to be placed in a piece of paper. Some RFID chips are made to be imbedded in livestock, in pets and most recently in humans for a variety of reasons. RFID prices have dropped, and tagging has become practical for businesses. In-Stat, a high-tech research firm, reports more than 1 billion RFID chips were made last year and predicts that by 2010 the number will increase to 33 billion. Slightly larger than a grain of rice, RFID chips from VeriChip of Florida are manufactured for implanting in humans. The Food and Drug Administration approved human implants two years ago.