The Smart Sock 2 Baby Monitor intelligently tracks your baby's heart rate and oxygen levels while they sleep. You'll be notified with lights and sounds if something appears to be wrong. Using Owlet's app, you can view real-time wellness data and receive direct notifications on your phone. Parents who use the Smart Sock sleep better and worry less—it's simply a smarter way to keep a close eye on your baby. Retails brand new for over $300. This one comes with all three sizes of socks plus an extra size 1. It also comes with 3 cords to connect base to monitor. Used until my daughter was 2 years old, I loved this.