Size S/M arm band. Used in original box. Works fine. No longer needed as I used it to help me conceive my first due to PCOS (now have two babies)! ALL-IN-ONE OVULATION TRACKING with Tempdrop 2.0✔️Tempdrop’s wearable sensor and charting app provide a comprehensive fertility charting solution right on your smartphone. With a quick 10-second data sync and automatic firmware updates, Tempdrop 2.0 ensures you have the most accurate and up-to-date information. Whether you want to increase your chances of conceiving or simply track your health, Tempdrop 2.0 is designed for you SLEEP IN, NO PROBLEM ✔️Tempdrop continuously monitors your basal body temperature (BBT) while you sleep, allowing you to understand your cycle without the need to wake up at the same time every day. EASY TO USE ✔️ Simply wear the Tempdrop sensor on your upper arm during sleep and sync at your convenience. Tempdrop 2.0 features simplified battery replacement, so you won’t have to worry about daily charging. COMPLETE DATA FREEDOM ✔️View and track your fertility signs using Tempdrop’s app (available on iOS and Google Play) or input your data into other fertility apps. The built-in charting features allow you to track multiple fertility signs and identify your cycle phases. Enjoy the freedom of complete data control with a seamless 10-second data sync and automatic firmware updates.