How wearable hormone tracking works
How wearable hormone
tracking works
How Phira works
Your hormones change how your body regulates heat and energy. Phira was built to listen to those signals 24/7.
Your hormones change how your body regulates heat & energy.
Phira was built to listen to those signals 24/7.
Your hormones change how your body regulates heat and energy. Phira was built to listen to those signals 24/7.
22%
Calendar apps ovulation prediction accuracy¹
Calendar apps ovulation prediction accuracy¹
68%
General wellness wearable ovulation prediction accuracy²
General wellness wearable ovulation prediction accuracy²
±8 days
Average ovulation variation cycle to cycle³
Average ovulation variation cycle to cycle³
6 days
Actual length of the fertile window
Actual length of the fertile window
The limits of averages.
The limits of averages.
Current cycle-tracking methods are limited to cycle phase detection, done based on averages. They lean on what happened last month, and then wait to confirm that ovulation has already happened.
But cycles shift month-to-month.³ And knowing roughly what phase you're in isn't the same as knowing your hormone patterns.
22%
Calendar apps ovulation prediction accuracy¹
68%
General wellness wearable ovulation prediction accuracy²
±8 days
Average ovulation variation cycle to cycle³
6 days
Actual length of the fertile window
The limits of averages.
Current cycle-tracking methods are limited to cycle phase detection, done based on averages. They lean on what happened last month, and then wait to confirm that ovulation has already happened.
But cycles shift month-to-month.³ And knowing roughly what phase you're in isn't the same as knowing your hormone patterns.
Your monthly rhythm.
Your monthly rhythm.
Across each cycle, these three hormones don't just change in blood. They shape how your body regulates temperature, circulation, and metabolic activity.
Estrogen
Role: Rising estrogen signals the approach of ovulation and the opening of the fertile window.
Thermoregulatory effect: Promotes peripheral vasodilation and affects the hypothalamic temperature set point, creating measurable thermoregulatory patterns that emerge before ovulation.
LH
Role: The LH surge triggers ovulation, typically occurring 24-36 hours before egg release.
Thermoregulatory effect: The LH surge is associated with distinct temporal patterns in thermoregulatory signals, detectable as a transition point in continuous thermal data.
Progesterone
Role: Progesterone rises after ovulation. Its presence & stability are key indicators of cycle health.
Thermoregulatory effect: Raises core body temperature, producing the well-studied post-ovulatory temperature shift. Its decline at the end of the luteal phase is an early signal of approaching menstruation.
Your monthly rhythm.
Across each cycle, these three hormones don't just change in blood. They shape how your body regulates temperature, circulation, and metabolic activity.
Estrogen
Role: Rising estrogen signals the approach of ovulation and the opening of the fertile window.
Thermoregulatory effect: Promotes peripheral vasodilation and affects the hypothalamic temperature set point, creating measurable thermoregulatory patterns that emerge before ovulation.
LH
Role: The LH surge triggers ovulation, typically occurring 24-36 hours before egg release.
Thermoregulatory effect: The LH surge is associated with distinct temporal patterns in thermoregulatory signals, detectable as a transition point in continuous thermal data.
Progesterone
Role: Progesterone rises after ovulation. Its presence & stability are key indicators of cycle health.
Thermoregulatory effect: Raises core body temperature, producing the well-studied post-ovulatory temperature shift. Its decline at the end of the luteal phase is an early signal of approaching menstruation.
What Phira detects.
Rather than tracking a single daily temperature readings or deviations, Phira continuously captures four overlapping physiological signals. The pattern across all four that reveals your hormone patterns.
Thermoregulatory dynamics
Thermoregulatory dynamics
The pattern of how your body regulates heat before, during, and after ovulation
Overall temperature patterns
Overall temperature patterns
The full thermal trajectory across the cycle, not just the post-ovulatory shift.
Thermal distribution
Thermal distribution
Changes in heat distribution that are detectable behind the ear where the superficial temporal artery sits close to the skin surface.
Changes in vasodilation that are detectable behind the ear above the superficial temporal artery.
Thermogenic shifts
Metabolic heat
production
Distinct and measurable short-term and long-term changes in metabolic heat production that reflect lifestyle events as they happen in real-time.
Distinct and measurable short-term and long-term changes in metabolic heat production.
What Phira detects.
Prior research with invasive intra-vaginal sensors showed that core body temperature and thermoregulatory patterns shift with hormonal changes. Phira is designed to capture these signals non-invasively, across your full cycle.
Thermoregulatory dynamics
The posterior ear is a clinical-grade site for measuring core body temperature, unlike extremities like the wrist or finger
Overall temperature patterns
Sensors accurate to 0.03°C detect subtle thermoregulatory shifts correlated with hormonal changes.
Thermal distribution
Changes in heat distribution that are detectable behind the ear where the superficial temporal artery sits close to the skin surface.
Thermogenic shifts
Daily updates on your hormones and what that means for your cycle, energy, fertility window & wellbeing.
Why behind the ear?
The superficial temporal artery runs upward behind the ear, approximately 1mm beneath the skin's surface. This superficial positioning enables the direct capture of thermoregulatory dynamics. Because these signals are tightly coupled to endocrine regulation, metabolic state, exercise response, & sleep, the posterior ear provides a stable and information-rich window into real-time physiological change.
The hormone changes we're designed to detect are subtle, we're looking for shifts of fractions of a degree. That's why sensor location matters as much as sensor quality. The Phira sensor is highly accurate and designed specifically to minimize motion artifact, environmental interference, and thermal noise. This enables precise, high frequency readings that actually capture physiological changes.
Less noise. Fewer artifacts. Deeper insights.
Why behind the ear?
The superficial temporal artery runs upward behind the ear, ~1mm beneath the skin's surface. This positioning enables direct capture of vascular and thermoregulatory dynamics which are tightly coupled to real-time endocrine regulation, sleep, exercise response, & metabolic state.
The hormone changes we're designed to detect are subtle, we're looking for shifts of fractions of a degree. That's why sensor location matters as much as sensor quality. The Phira sensor is highly accurate and designed specifically to minimize motion artifact, environmental interference, and thermal noise. This enables precise, high frequency readings that actually capture physiological changes.
Less noise. Fewer artifacts. Deeper insights.
Your cycle reflects your life.
Your cycle reflects your life.
Sleep deprivation, chronic stress, high training loads or limited physical activity, and nutritional imbalances all affect hormonal output. The relationship runs both ways, your hormone patterns shape how you respond to these factors, and these factors shape what your hormone patterns. Phira is designed to help you see both sides of that relationship.
Sleep
Poor or disrupted sleep elevates cortisol and suppresses LH pulsatility, directly impacting ovulation timing and cycle regularity. Published research links chronic sleep disruption to hormonal imbalance.
Poor or disrupted sleep elevates cortisol and suppresses LH pulsatility, directly impacting ovulation timing and cycle regularity. Published research links chronic sleep disruption to hormonal imbalance.
Stress
Cortisol and the HPA axis interact directly with the HPG axis that governs reproductive hormones. Chronic psychological stress can suppress ovulation, shorten the luteal phase, and disrupt cycle regularity.
Cortisol and the HPA axis interact directly with the HPG axis that governs reproductive hormones. Chronic psychological stress can suppress ovulation, shorten the luteal phase, and disrupt cycle regularity.
Training
Relative Energy Deficiency in Sport (RED-S) and overtraining are well-documented drivers of hypothalamic amenorrhea and anovulatory cycles. Monitoring training load alongside cycle data helps identify risk earlier.
Relative Energy Deficiency in Sport (RED-S) and overtraining are well-documented drivers of hypothalamic amenorrhea and anovulatory cycles. Monitoring training load alongside cycle data helps identify risk earlier.
Nutrition
Caloric restriction and micronutrient deficiencies affect hormone production. Body fat percentage influences estrogen metabolism. Understanding the nutritional inputs alongside your hormones creates a more complete picture.
Caloric restriction and micronutrient deficiencies affect hormone production. Body fat percentage influences estrogen metabolism. Understanding the nutritional inputs alongside your hormones creates a more complete picture.
For health & wellness
For health & wellness
Understand your body beyond your period.
Women are often told to live with symptoms rather than understand them. Phira shows you the hormonal pattern behind your cycle, tune into your body to put yourself back in control every month.
Understand your body beyond your period.
Women are often told to live with symptoms rather than understand them. Phira shows you the hormonal pattern behind your cycle, tune into your body to put yourself back in control every month.
For longevity.
For longevity.
Your patterns today shape your health for decades.
Hormones are a thread running throughout your life. Phira tracks those patterns continuously, building a record of your hormonal patterns over time.
Your patterns today shape your health for decades.
Hormones are a thread running throughout your life. Phira tracks those patterns continuously, building a record of your hormonal patterns over time.
Why behind the ear?
Why behind the ear?
The superficial temporal artery runs upward behind the ear, approximately 1mm beneath the skin's surface. This superficial positioning enables direct capture of vascular and thermoregulatory dynamics. Because these signals are tightly coupled to endocrine regulation, metabolic state, exercise response, and sleep, the posterior ear provides a stable and information-rich window into real-time physiological change.
The hormone changes we're designed to detect are subtle, we're looking for shifts of fractions of a degree. That's why sensor location matters as much as sensor quality. The Phira sensor is highly accurate and designed specifically to minimize motion artifact, environmental interference, and thermal noise. This enables precise, high frequency readings that actually capture physiological changes.
Less noise. Fewer artifacts. Deeper insights.
Get in tune with your body.
Join the waitlist to be part of the research behind Phira
Get in tune with your body.
Join the waitlist to be part of the research behind Phira
Get in tune with your body.
Join the waitlist for early access and the chance to be part of the research behind Phira.
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 A. Maijala et al., "Nocturnal finger skin temperature in menstrual cycle tracking: ambulatory pilot study using a wearable Oura ring," BMC Women's Health, vol. 19, no. 1, p. 150, Nov. 2019, Art. ID 150
⁴ 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.