Tempdrop 2 Advanced Fertility Monitor, L/xl

All you need to do is wear the Tempdrop device on your upper arm while you sleep. The device contains multiple sensors that measure your core temperature continuously throughout the night, and their patented algorithm learns your unique nightly and monthly temperature patterns, filtering out disturbances for more accurate results.

You can also track any ovulation symptoms you have in the app, and when combined with your Tempdrop temperature readings, it can more accurately identify when you may be ovulating.