Continue to enjoy a sense of security with your Smart Sock 3. With the supplemental package, you can keep monitoring your child's heart rate, oxygen levels, and sleep habits from birth up to the age of 5. The included toddler-sized fabric socks work with your existing Smart Sock 3 sensor, and optimized technology continues to provide accurate readings as your child grows - weighing between 13.5 kg and 25 kg. Keep tracking your child from milestone to milestone - from teething to the tooth fairy.