Tempdrop is a wearable thermometer that's popular among menstrual cycle charters.
Enjoy a 10% discount on your Tempdrop thermometer with the offer code RYBLOVE10
It consists of a sensor and an armband. You wear it on your upper arm while you sleep. It takes thousands of temperature readings while you sleep and generates a single basal body temperature value for you after each sleeping session.
It's especially useful for those with irregular sleeping patterns / waking routines as it filters out motion while you wear it to find the most stable resting reading and it doesn't require you to wake up at the same time each day. It's appreciated by many shift workers, nursing parents and those with busy lifestyles.
Tempdrop gives $15 to support the non-profit development of Read Your Body whenever this code is redeemed.