Daysy doesn't guess. It measures a specific physiological signal at a specific time, with a precision tied to peer-reviewed research. This page tells you exactly what that signal is and why we read it the way we do.
After ovulation, your body releases progesterone. Progesterone raises your baseline temperature by roughly 0.5°F. That rise is small, fast, and only detectable if you measure at the right place, at the right time, with enough precision.
The right place is under the tongue, where the temperature is closer to your core body temperature than at the wrist or finger. The right time is the moment you wake, before metabolic activity changes the reading. The right precision is ±0.05°C, the threshold below which the post-ovulation rise becomes detectable in real-world data.
Daysy measures all three.
The rise is roughly 0.5°F (about 0.27°C). Detecting it reliably requires a thermometer precise to at least ±0.05°C.
In 2021, van de Roemer, Haile, and Koch published a study of Daysy's algorithm in a peer-reviewed journal. Here's what it actually established.
The study did not establish Daysy as a contraceptive device. It did not measure contraceptive efficacy. It measured the algorithm's ability to correctly identify cycle phase, not its ability to prevent pregnancy. Daysy is not a contraceptive. The honesty page says more about this.
Reference: van de Roemer N., Haile L., Koch M. (2021). Performance evaluation of Daysy.
Daysy is a Class I registered medical device. Class I is the FDA's pathway for low-risk devices. Lady-Comp goes a step further and is FDA 510(k) cleared, a higher regulatory standard.
"Registered" is different from "cleared" and "approved." Class I registration means the FDA knows the device exists and the manufacturer meets general controls. 510(k) clearance means the device has been compared to an existing approved device. PMA approval means the device has been independently evaluated for safety and efficacy. Daysy is registered. Lady-Comp is cleared. Neither is PMA-approved.
We use these terms exactly the way the FDA uses them. Read the full regulatory breakdown.
Read the science once. Then decide.
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