What's Included: 3 fabric socks, sensor, base station, chargers Owlet's updated sock sensor is flexible and designed to adapt to your baby?s foot as he or she grows. Updated pulse oximetry algorithms increase the precision and accuracy of your baby?s readings. Designed for a better fit and placement, meaning more accurate readings. Hypoallergenic cotton gently wraps around your baby?s foot, and the sock can be worn on either foot, allowing parents to alternate as needed. Bluetooth range, up to a 10x increase (100 feet), between the Smart Sock and Base Station. interface with sock sizing guide, push notifications and real time access to your baby?s heart rate and oxygen levels.