The science of subtlety
Most cycle tracking methods rely on calendar predictions which estimate ovulation correctly only 22% of the time1. Even in individuals with seemingly regular cycles, ovulation varies by an average of ±8 days from one cycle to the next2.
By measuring your body’s unique vascular and thermogenic signatures, our smart earring-back captures how estrogen, progesterone, and luteinizing hormone shape your physiology across each phase of your cycle. Instead of guessing, we map your hormones as they shift in real time — giving you a precise, personalized window into your metabolic health, fertility, and long-term reproductive goals.
Most cycle tracking methods rely on calendar predictions which estimate ovulation correctly only 22% of the time1. Even in individuals with seemingly regular cycles, ovulation varies by an average of ±8 days from one cycle to the next2.
By measuring your body’s unique vascular and thermogenic signatures, our smart earring-back captures how estrogen, progesterone, and luteinizing hormone shape your physiology across each phase of your cycle. Instead of guessing, we map your hormones as they shift in real time — giving you a precise, personalized window into your metabolic health, fertility, and long-term reproductive goals.
Your Monthly
Hormonal Rhythm
Across each cycle, estrogen rises leading up to ovulation, luteinizing hormone (LH) surges to trigger ovulation, and progesterone increases afterward to support the luteal phase. These hormones don’t just change in blood, they change how your body regulates heat, blood flow, and metabolic activity.
Estrogen
Earliest signal of high fertility
LH
Marks the ovulatory transition
Progesterone
Confirms ovulation occurred
Estrogen
Earliest signal of high fertility
LH
Marks the ovulatory transition
Progesterone
Confirms ovulation occurred
Your physiology shifts before, during, and after ovulation — and those shifts are measurable.
Female Hormones
Estrogen and progesterone significantly impact your body’s vascular tone, thermoregulation and metabolic heat production3.
Rather than observing single basal body temperatures, Phira continuously tracks the patterns that reveal your hormonal shifts:
Thermoregulatory dynamics
Peripheral vascular changes
Overall temperature patterns
Thermogenic shifts
Thermoregulatory dynamics
Peripheral vascular changes
Overall temperature patterns
Thermogenic shifts
These signals together reflect underlying hormonal transitions while also providing insight into sleep, exercise and nutrition.
Estrogen and progesterone significantly impact your body’s vascular tone, thermoregulation and metabolic heat production3.
Rather than observing single basal body temperatures, Mirie continuously tracks the patterns that reveal your hormonal shifts:
Thermoregulatory dynamics
Peripheral vascular changes
Overall temperature patterns
Thermogenic shifts
Thermoregulatory dynamics
Peripheral vascular changes
Overall temperature patterns
Thermogenic shifts
These signals together reflect underlying hormonal transitions while also providing insight into sleep, exercise and nutrition.
Female Hormones
Estrogen and progesterone significantly impact your body’s vascular tone, thermoregulation and metabolic heat production3.
Rather than observing single basal body temperatures, Phira continuously tracks the patterns that reveal your hormonal shifts:
Thermoregulatory dynamics
Peripheral vascular changes
Overall temperature patterns
Thermogenic shifts
These signals together reflect underlying hormonal transitions while also providing insight into sleep, exercise and nutrition.
Mapping the Cycle in Real Time
The fertile window begins 4 days before ovulation
Peak fertility begins 2-3 days before.
For contraception
Because hormone-driven physiological changes begin days before ovulation, Phira detects the early thermoregulatory and vascular shifts that signal the opening of the fertile window in real-time.
Knowing when to avoid can reduce chances of pregnancy by up to 13% compared to barrier methods alone which are only 85% effective with typical use4,5.
For conception
As the body prepared for egg release, estrogen rises, indicating high fertility. By precisely detecting this early hormonal shift, Phira provides advance insight into ovulation, days before traditional urine-based LH tests turn positive.
For conception, this can boost pregnancy chances by up to 30%6.
For contraception
Because hormone-driven physiological changes begin days before ovulation, Phira detects the early thermoregulatory and vascular shifts that signal the opening of the fertile window in real-time.
Knowing when to avoid can reduce chances of pregnancy by up to 13% compared to barrier methods alone which are only 85% effective with typical use4,5.
For conception
As the body prepared for egg release, estrogen rises, indicating high fertility. By precisely detecting this early hormonal shift, Phira provides advance insight into ovulation, days before traditional urine-based LH tests turn positive.
For conception, this can boost pregnancy chances by up to 30%6.
Phira integrates temperature, thermogenic response, and vascular signatures into hormone modeling algorithms trained on longitudinal cycle data.
Phira integrates temperature, thermogenic response, and vascular signatures into hormone modeling algorithms trained on longitudinal cycle data.
Instead of predicting based on past cycles, we interpret your physiology as it changes — in real time. The result?
Continuous hormonal insight grounded in biology.
[1] S. Johnson, L. Marriott, and M. Zinaman, “Can apps and calendar methods predict ovulation with accuracy?,” Current Medical Research and Opinion, vol. 34, no. 9, pp. 1587–1594, May 2018.
[2] C. Kryder, “How Oura Data Can Help You Understand Your Menstrual Cycle,” The Pulse Blog, Apr. 25, 2023.
[3] N. Charkoudian and N. S. Stachenfeld, “Reproductive hormone influences on thermoregulation in women,” Comprehensive Physiology, vol. 4, no. 2, pp. 793–804, Apr. 2014, doi: https://doi.org/10.1002/cphy.c130029.
[4] Cleveland Clinic, “Birth Control Options & types: Risks & Effectiveness,” Cleveland Clinic, Aug. 18, 2022.
[5] E. Benhar, Agathe van Lamsweerde, K. Krauss, E. B. Scherwitzl, and Raoul Scherwitzl, “Contraceptive Outcomes of the Natural Cycles Birth Control App: A Study of Canadian Women,” Sep. 16, 2024.
[6] S. Johnson, L. Marriott, and M. Zinaman, “Increased Likelihood of Pregnancy from Sex on the Two Days Before Ovulation [5B],” Obstetrics & Gynecology, vol. 131, no. 1, pp. 20S20S, May 2018.