Understand every night,
see daytime stress.

Core Concept

Compared with your past 28 nights, not other people

Each metric has a usual range of your own, calculated from the median and robust dispersion of your past 28 nights. A single extreme night does not widen the range; only three consecutive nights deviating in the same direction are treated as a new usual.

Screens

Clear the moment you open it

All screens below show the app’s built-in demo data, not anyone’s real values.

← Swipe horizontally →

Features

What you can do today

How It Works

From your wrist to a single line each morning

1. Sleep with your Apple Watch

   The watch records heart rate, HRV, respiratory rate, blood oxygen, and wrist temperature overnight, saving them to Health on your iPhone. Photophore only reads this data and modifies no records.

2. Compare with your past 28 nights

   When you wake up, each metric from that night is compared with the median and robust dispersion of your past 28 nights; checks begin once you accumulate 7 nights.

3. See what differed from usual

   Metrics outside your usual are flagged, showing how much they differ, common contributing factors, and research sources. During the day, HRV estimates stress, producing provisional scores at 3 days and official ones at 7 days.

Principles

How we build this app

Every number has a source

The Method page lists every threshold and its research source; starting values without direct research support are honestly labeled “unvalidated.”

Your data stays with you

No servers, no accounts, and no iCloud. All calculations take place on your iPhone and Apple Watch.

Read only, never write

Photophore only reads data from Health and never modifies or writes to your health records.

No diagnoses

It helps you spot what is “outside usual,” without diagnosing causes or replacing a doctor.

Name Origin

A row of lights in the deep sea

Photophore

Greek phōs (light) + phoros (bearer)
A light-emitting organ

A photophore is a light-emitting organ found on deep-sea creatures. Lanternfish carry rows of photophores along their bellies. In the deep ocean where sunlight barely reaches, these small points of light help them hide their silhouettes and recognize one another.

While you sleep, your body leaves signals in the dark: heart rate, respiratory rate, blood oxygen, and HRV. Photophore lines them up as points of light, one for each metric; the one outside usual glows.

Roadmap

Lighting up step by step

Glowing dots are completed milestones, half-lit dots are undergoing on-device testing, and hollow dots are up next.

1. Completed

2. Seven Overnight Vitals and Personal Baselines

   Completed

   Seven overnight metrics, 28-night usual ranges, calibration progress, and research explanations for each metric.

3. Daytime Stress Score

   Completed

   Scores and levels converted from HRV, personalized mappings, all-day curves, and exclusion rules for walking and workouts.

4. Background Updates

   Completed

   Without opening the app, your iPhone updates in the background and sends results to your watch.

5. How Are You Feeling

   Completed

   Fatigue and tension check-ins, along with condition tags for the day.

6. TestFlight Beta

   Open

   Approved by Apple’s Beta App Review, and the build has every feature turned on. Install Apple’s TestFlight app, then join using the public link; the privacy policy is live.

7. On-device testing

8. Apple Watch App, Watch Faces, and Widgets

   On-device testing

   The watch calculates the stress level on its face in the background; iPhone Lock Screen and StandBy widgets.

9. Unusual Days Do Not Skew Your Usual

   On-device testing

   Days with alcohol, illness, or temporary medication appear normally, but are excluded from the usual range used for future comparisons; when regular medication changes, the baseline is rebuilt from that day forward. Day counts are set according to research recommendations.

10. Morning Recovery Check

    On-device testing

    Take a 30-second reading upon waking with Apple’s ECG app; Photophore calculates HRV using only beat-to-beat intervals from sinus rhythm recordings to track a 7-day rolling average. It does not interpret heart rhythm.

11. More Watch Faces and Widgets

    On-device testing

    Large stress widgets with daily level ratios, cooldown countdowns after workouts or walking, “Last night” and “HRV” watch faces, with past 7-day and morning values on the watch; the watch app curve continues showing the past 24 hours past midnight.

12. Stress Notifications

    On-device testing

    Notifies you when stress rises significantly, drops, fluctuates notably within an hour, stays low for an hour, or stays high for half an hour; a morning notification also tells you what differed from usual last night. Titles include the HRV, stress level, and timestamp, with the past 2 hours of curves attached. When iPhone is locked, Health cannot be read, so missed notifications are delivered upon unlocking; if iPhone has not checked for too long, the watch sends them instead. Stress notifications support Quiet Hours and do not send during sleep.

13. Calculating “A Night” Around Your Schedule

    On-device testing

    When your schedule shifts noticeably late or early, the night’s time window shifts with your sleep over the past two weeks, counting the entire sleep session into the same night.

14. Heart Rate Recovery Time After Walking

    On-device testing

    How many minutes it took for your heart rate to return to your usual resting level after each walk, alongside Apple’s Cardio Recovery and Cardio Fitness estimates, placed side by side with a full year of HRV. Focuses solely on your own trends, without labeling them good or bad.

15. Up next

16. Personal Calibration

    After data accumulates

    Compare three to four weeks of check-in records against stress scores to verify whether thresholds match your actual feelings before adjusting.

17. Under evaluation

18. On-Demand Measurements on the Watch

    Under evaluation

    Start a brief measurement directly from the app to see your current state immediately.

19. Period Annotations

    Optional · Under evaluation

    Off by default; when enabled, annotations appear only on days with logged records, without inferring cycle phases.

FAQ

Questions you might have

How do I join the beta?

First install Apple’s TestFlight app on your iPhone, then open the public link to install Photophore; the watch app installs alongside it, or can be installed from the Apple Watch app on your iPhone. You can submit feedback via “Send Beta Feedback” in TestFlight, or by emailing photophore@nyanako.com.

What devices are required?

iPhone (iOS 27) and Apple Watch (watchOS 27). Overnight metrics require wearing your watch to sleep.

How soon will I see results?

Overnight metrics begin checks once 7 nights have accumulated, with a complete baseline after 28 nights; stress scores produce provisional values at 3 days and become official at 7 days.

Is data uploaded anywhere?

No. There are no servers and no accounts; all calculations happen on your iPhone and Apple Watch, and nothing goes to iCloud.

Will it send notifications constantly?

Notifications are off by default and must be turned on in Settings; each type can be toggled independently. On the same device, a given state triggers only one notification; if several stress notifications trigger at once, only one is sent, and persistently elevated stress notifies at most once every half hour. Stress notifications do not send during Quiet Hours (default 22:00 to 08:00) or while sleeping. When iPhone’s “Show Previews” remains at its default, the Lock Screen only displays “New Notification”.

Is it accurate?

Apple Watch measurements carry their own margins of error, and most of Photophore’s thresholds are research-recommended starting values. The Method page lists sources and unvalidated elements item by item; it is suited for observing your own trends, not for medical diagnosis.