Body Alert, Immunity, Breathing and safety alerts

What these indices are#

Resilience is Body Alert turned around: 100 minus Body Alert. It is the name on the Health tab card and on the Body Status tile, where a higher number has to mean a better day. A Body Alert of 18 is a Resilience of 82.

None of these measures an infection. A watch cannot measure immune cells or inflammation. What it can see is the pulse, the HRV, the breathing rate, the blood oxygen and the skin temperature of the night, and what often happens to them in the days around an infection. The same changes also come with a hard training block, a poor night, alcohol, stress, travel or the second half of a menstrual cycle. So the index is a reason to look at your day, not an answer to what is wrong.

Where you see them#

• Overview: the card "Body Alert" with a ring, a band word, a short sentence, a short trend line, "Worsened most by", the "Signals watched" fold and, on the same card, the Overtraining bar (training load). Tapping the ring opens "How the number is built".
• Health tab: the six cards beside the body figure include "Immunity", "Breathing" and "Resilience".
• Body Status: the tile "Resilience" and the tile "Immunity" under "What the state stands on", and the verdicts Alert and Recovering (Body Status).
• Sleep tab: the card "Breathing" (blood oxygen, snoring, apnea index) and the card "Overnight physiology" (HRV, resting heart rate, breathing rate, blood oxygen and skin temperature on one axis).
• Alerts: the banners at the top of the Overview, see Safety alerts.

The cards on the Health, Sleep and Overview tabs are Premium, the safety alerts are not. See Free and Premium.

Body Alert#

The nine signals#

Body Alert reads trends over a 7-day window: the newest 3 calendar days against the days before them. A trend needs at least 4 readings across the two halves and some in each. If fewer than 4 of the last 7 days carry a resting rate, stress or sleep, the window widens to 14 days.

Each sub-score runs from 0 to 100 and only counts the way that signals trouble: a falling pulse is not a sign. A night of deep sleep that fell to nothing is a reading, the full collapse it is, and not "no data". A signal your device does not measure is missing, not zero.

• Resting heart rate. If your resting rate rose from 57 to 61 over the last 3 days and your 30-day spread is 4 bpm, half of it is 2, so the divisor is 2, and the sub-score is 4 / 2 × 30 = 60.
• HRV. The nights' average, in the same window, against the nights before. A fall of 16 % gives 32; 50 % or more fills it. It reads the device's nights of one device (HRV).
• Blood oxygen. A level held for weeks is your wrist's, not an illness, so against at least 10 older nights of the month, a night no more than 1.5 points under their median is capped at 10, provided it is 88 % or higher. Under 88 % stays as scored.
• Overnight recharge and morning energy are Body Battery from Garmin, its 0 to 100 energy level. They are missing on other devices, and the other signals carry the index.

From the signals to the number#

1. Weighted average. The sub-scores are averaged by weight, over the signals you have. The weights add up to 108, so each is divided by the total present.
2. Thin data. With 2 signals the average keeps 60 % of its distance from 50, with 3 signals 80 %, with 4 or more all of it. With a single signal it stands as it is.
3. Floors. Three absolute levels set a floor the index cannot fall under (see Floors).
4. Surcharges. A reported illness, acute-illness medication and a warm night skin add points, in total at most 20 (Surcharges).
5. Fast moves. A rapid fall of HRV and a jump in the resting rate overnight add a little (Fast moves).
6. Low mornings. A run of low mornings adds 8 or 15 (Low mornings).
7. The result is rounded and held between 0 and 100.

The sheet "How the number is built" shows each step as a bar of points, ending on the number on the ring. It also lists each signal's recent and older value, its change and its share of the weight, and the floors.

Floors#

A body that is persistently low on HRV, high on resting rate or low on morning energy is not calm just because nothing is changing. So three levels, read over the 7 days (14 if the window widened), set the least the index can be:

• The HRV norm is a study of overnight RMSSD in people of each age and sex (Natarajan and colleagues, 2019 preprint). For a 40-year-old man the 25th percentile is about 27 ms, the 10th about 20 and the 2.5th about 14. A woman is a little lower. With no known age we assume 40.
• The resting rate is adjusted before it is compared: 5 bpm is taken off for women and 0.15 bpm for every year of age past 30. A 40-year-old man's floor of 12 starts at an average above 66.5 bpm.
• The sheet prints each level with the floor it gave ("floor 18, applied").

Surcharges#

• Reported illness. A check-in that says you are unwell, dated today or in the 3 days before, and not taken back by a newer check-in that says you are not. It adds 6 times a weight from your severity answer: severity 1 gives 6, 2 gives 8, 3 gives 9, 4 gives 12, 5 gives 15. With no severity (the quick "Ill" button) we use 3, so 9.
• Acute-illness medication. A check-in dated today or in the 2 days before that says you took medication of the type "Acute illness" adds 3. Preventive, supplement and chronic medication do not count ("Only medication for an acute illness affects Body Alert").
• Skin temperature. A night with the skin warmer than your own 30-day level by at least 2 of your own night-to-night spreads, or by 1.0 degree or more, adds 14. At least 1 spread adds 8. With no spread yet, 0.5 degree adds 8.
• The three together never add more than 20, and the index never exceeds 100.

Fast moves#

• Falling HRV. The slope of your last 7 nights, read at a reference of 40 ms: a fall of more than 3.0 ms a day is worth 12 points and more than 1.5 ms a day 5. We add only what exceeds the points the HRV signal already gave the same fall, so one fall counts once.
• Overnight jump of the resting rate. If today's resting rate is more than 5 bpm above yesterday's (two consecutive days, the newer being the scored day), 8 points.

Low mornings#

A morning energy below your usual by more than one of your own spreads counts as low. Three or four of them in a row add 8, five or more add 15 (Morning Energy).

Reading the number#

The Czech words are "Vše v pořádku", "Nízké riziko", "Střední riziko", "Zvýšené riziko" and "Vysoké riziko". The words describe how many of your signals have moved, and the card says so: "A 0 to 100 index; higher means more warning signals ... Not a medical diagnosis."

• A sentence under the ring follows the number: "No warning signals in today's data.", "Small deviations in your signals, nothing substantial yet.", or "Today's data show warning signals." A low number with one signal worsening reads "One signal is worsening; the overall index stays low."
• "Worsened most by" lists up to 3 signals whose sub-score is 40 or more, ranked by their share of the points.
• "Signals watched" lists each signal with a word: from 20 "slight shift", from 40 "worsening". Blood oxygen is a level, so its words are "slightly low" and "low". The fold's summary counts, for example, "2 of 9 worsening".
• Body Status treats 55 and above as one of its Alert channels, and a value under 45 as part of the floor under Strong and Peak Day (Body Status). Several channels, or a second day of the same one, are needed before it says Alert.
• When the signals behind the index are too old, the ring is empty and says "No current data" and "Last measured 28/10".
• Fewer than 5 days of data in the last 30 gives no Body Alert. A device with no overnight biosignals shows the Overtraining card under its own name.

Several signals at once#

Beneath the index, the card can show one more box, marked "estimate", with a title such as "Several signals at once · low risk", a one-line message and "Signal strength: mild". It is a count of how many separate signals have moved together over the last 3 days against the 11 days before, and it appears only when at least 2 have and you have at least 7 days of data in the last 14. Body Status counts 3 or more of them as its Alert channel even when the index is under 55.

One physical channel counts once: a drop of HRV, a steep slope of HRV and a 3-day pattern built from the same HRV are one HRV signal. In your check-in, acute-illness medication counts only when a measured signal agrees, and low energy counts for half as much when none does.

The box works out a strength: 15 + 8 for each signal + 12 times how large they are, at most 85, and times 0.6 when you did a session of more than 30 minutes at a moderate or high level yesterday, unless your HRV is falling fast. The number is never shown. You see its band: 65 or more "high", 45 or more "elevated", 25 or more "mild", below that "low", and the title's word "high risk", "medium risk", "low risk" or "minimal risk". Under 3 separate signals it adds "limited data yet". The message is "Your body shows signs of strain. Take a few easier days and notice how you feel." or, when you reported being ill, "You reported being ill. Rest and keep an eye on your symptoms."

The same box can instead name "Exhaustion" (your morning energy of the last 7 days falling by a quarter between the first and second half, while stress is above 40 or not measured) or "Sleep disruption" (your last three sleep scores more than 10 points under your first three). The box shows the strongest of the three.

Your own earlier illnesses. When you report an illness in the check-in and we hold the data, we store a fingerprint of the days before it: the changes in resting rate, HRV, morning Body Battery, stress, blood oxygen and sleep score over days 3 to 7 before it, against days 8 to 21 before. Later, the last 17 days are compared with these. Unticking the illness removes the fingerprint. It needs at least 3 shared signals of a real size to say anything.

Immunity#

Immunity ("Imunita") reads the signals the literature links with resisting illness: deep, good sleep, overnight HRV, blood oxygen, morning energy and resting heart rate. The card says what it is not: "A watch cannot measure immune cells or inflammation; this is their indirect picture."

• HRV. The trend half is 50 + (recent / older - 1) × 150, so 12.5 % lower is 31. The level half is the ladder of the recent nights, shifted by where they sit among your own nights (HRV). It needs at least 5 nights across the two sides.
• Blood oxygen ladder. 96 % and above 90 to 100, 94 to 96 % 75 to 90, 92 to 94 % 55 to 75, down to 15 at 88 % and 0 at 80 %. The newest night shifts it by up to 20 points against your own month.
• Body Battery trend. A rising line scores 80, a fall of under 1 point a day 50, 1 to 3 points a day 30, more than 3 points a day 10. It needs 3 mornings.
• Charge against drain. A ratio of 1.3 or more 90, 1.0 to 1.3 70, 0.7 to 1.0 45, under 0.7 20.

After the average: a rising HRV slope (1.5 ms a day or more) adds 5, a steep fall (3.0 ms a day or more) takes 5. Then a resting-rate deduction against your 30-day usual: up to 3 bpm above it, nothing; from 3 to 5, rising from 0 to 8 points; above 5, 12; above 8, 25. With no usual yet, absolute lines apply instead (over 70 bpm, 78 and 85, with 5 bpm added for women).

The score needs at least 3 days of data and 2 in the last 7. With 2 or 3 parts it is pulled toward 50 as above.

Body Status uses Immunity (Strong needs above 60, 15 % of the dial, see Body Status).

Breathing#

Breathing ("Dýchání") is a 0 to 100 index of how your breathing behaves in sleep and rest, from the signals your device measures. It leans on what actually measures breathing: it needs at least one of breathing rate, apnea index, snoring, blood oxygen or the night's lowest oxygen. Deep sleep, stress and sleep efficiency alone never make a Breathing index, because they modulate breathing but say little about it.

Weights are shared out among what your device sends. After the average, a warm night skin takes points off (see below).

• Deep sleep. The share of your sleep spent in deep sleep over 7 days, against the target for your age: a man's is 20 % at 20, 17 % at 30, 15 % at 40, 12 % at 50, 9 % at 60, 7 % at 70; a woman's is 22, 20, 18, 15, 12 and 10 %; 15 % when age is unknown. The score is 50 + (share / target - 1) × 100: 14 % against 15 % gives 43. Nights with implausible stage totals are skipped.
• Apnea index. Events of paused or shallow breathing per hour of sleep, from devices that report it (Withings). The middle of the last 30 nights, because it is a chronic pattern and a median is not canceled by a run of quiet nights. Under 5 gives 95, 5 to under 15 gives 60, 15 to under 30 gives 30, 30 or more gives 10. The card's bands are "normal", "mild", "moderate" and "severe" (on the Sleep tab, in the card "Breathing"). It is a band, not a diagnosis.
• Breathing rate. If you have a 30-day usual and spread, the newest night's rate against your mean: 3.0 breaths a minute or more over gives 30, 1.5 or more over gives 60, anywhere from 1.0 under to just under 1.5 over gives 85, and more than 1.0 under gives 90. Without a usual: under 10 gives 30, 10 to 12 70, 12 to 20 85, 20 to 23 60, above 23 30.
• Night's lowest oxygen. The median of your nightly minima: 90 % or more gives 95, 87 to 90 80, 84 to 87 60, 80 to 84 35, under 80 10. Healthy sleepers dip to about 90 % at their lowest, and a watch's lowest reading sits a point or two below that, which is why the ladder is forgiving.
• Snoring. Under 5 % of the night 95, under 15 % 75, under 30 % 50, otherwise 25. Only a device with a microphone or a mat sends it.
• The breathing-disturbance index some devices report is shown on the sleep card, not scored.
• Skin temperature penalty. A night with the skin warmer than your 30-day level by 1.0 degree or more, or 2 of your own spreads, takes 20 points off the average. One spread takes 10. With no spread, 0.5 degree takes 10. It reads the night of the scored day only.

The night's numbers on the Sleep tab#

The Sleep tab's card "Breathing" prints last night's blood oxygen ("Blood oxygen 96 %, min 91 %"), snoring and apnea index, and 30-night strips for the apnea index and snoring (shown from 3 measured nights). Blood oxygen is colored good from 95 %, fair from 92 % and low below. The card "Overnight physiology" draws up to five signals (the row for breathing rate is called "Respiration rate") on one axis, each with your usual range (your average of the period plus and minus one standard deviation, from 7 nights), with a ring on nights outside it, and a line such as "3 of 5 signals moved together". The period is 14, 30 or 90 days. It says: "Several at once can mean illness, alcohol or strain. Not a medical diagnosis."

Skin temperature#

Skin temperature reaches us as a difference from your own baseline, in degrees: your device compares the night with your usual and sends how far off it was (Oura and Fitbit send nothing else, and a Garmin linked directly sends it too). We never compare it with anybody else's skin. In the card "Overnight physiology" it is the row "Skin temperature", signed (+0.30, -0.12), and in Fahrenheit the difference is multiplied by 1.8 without adding 32.

It is used in three places:

• as a surcharge to Body Alert: +8 from 1 spread, +14 from 2 spreads or 1.0 degree (Surcharges);
• as a penalty in Breathing: 10 or 20 points (Breathing);
• as a note on the Overview when the night was a whole degree or more above your usual: "Your skin temperature last night was 1.2 °C above your usual. That can come with a fever or an infection, and also with alcohol, a warm bedroom or, for women, the second half of the menstrual cycle. If you feel unwell, measure your temperature with a thermometer." For men the menstrual cycle is left out.

All three read the night of the scored day, never an older night.

Are you feeling ill? The check-in#

Your own word is the one signal a sensor cannot give. The check-in is where you give it. Under the Body Status verdict three buttons say "Fine", "Tired" or "Ill". The full form ("How were you feeling?") has energy, mood, physical, sleep quality and felt stress on 1 to 5, "Currently feeling unwell" with a type (Cold, Flu, Headache, Stomach, Allergy, Covid, Injury, Fatigue, Other) and a "Severity" from 1 to 5, "Took medication today" with a type, alcohol, and notes.

What an "unwell" answer does:

• Body Status: "Ill" makes the day Alert at once, with the advice to rest, drink and sleep, and see a doctor if it does not ease or gets worse. It stays open for 3 days until you say you are well (Body Status).
• Body Alert: a surcharge on that day and the 3 days after (Surcharges); a newer check-in saying you are not unwell takes it back.
• Several signals at once: counts as 3 signals and changes the message.
• Your earlier illnesses: stores a fingerprint of the days before (above).
• HRV: the row "When ill" in "What moves your overnight HRV" (HRV).
• Safety alerts: a check-in that says you are unwell today ("Ill", or "Tired" and a physical rating of 2 or lower) puts the blood-oxygen line back to 92 %, so a low night is read as new, and a low resting rate gets a fresh note.

"Tired" and the other answers are for you and for patterns we show you. They do not enter Body Alert, except low energy (1 or 2) as one of the signals in the box above.

Safety alerts#

Some readings outrank every score, because a body that crosses them may need a doctor and not a better day. They are read against fixed lines, not against your usual (except as noted). The first group, oxygen, blood pressure, resting rate and apnea, says the same words on the Overview banner, in the Body Status verdict and in the morning notification.

• Oxygen with your own normal. If your own month is itself low (median under 92 % on at least 14 nights), a single night under 92 % is not new. The line moves to your median minus 3, never lower than 88 % and never above 92 %. You are asked once to check it with a finger oximeter or a doctor, and you can answer "Checked, it is fine", "I live at altitude" or "Known lung condition, my doctor knows". A night under 88 % or a sudden fall is always flagged. At high altitude (above about 2,000 m) lower values are normal, and the text says so.
• What the words say. For oxygen: "If you feel short of breath or unwell, seek medical attention now. A wrist sensor is less accurate than a clinical device." For blood pressure at 180/110: measure again after five minutes of rest, contact a doctor today if it stays, and call emergency services with chest pain, shortness of breath, a severe headache or blurred vision. For a resting rate over 100: a fever, dehydration, some medicines or a heart rhythm problem can cause it, so see a doctor if it continues or you notice palpitations, dizziness or shortness of breath. For a rate under 40: in people who train for endurance it is common and healthy (answer "I train for endurance" or "My doctor knows"), and otherwise or with dizziness, fainting or unusual tiredness see a doctor. A rate under 30, or a further fall of 5 bpm, asks you to see a doctor.
• What they do to your day. A danger reading puts Body Status at Recovering at best, and never beside a Strong or Peak Day. A resting rate over 100 or a severe apnea index caps the day at Steady. The morning notification mentions a danger reading only when it is new, that is, when none of the 7 days before carried it, so a standing reading is not a daily alarm.
• At most three banners at once, danger first.

Heart sensor alerts#

Two other counts can appear on the Health tab in "Heart sensor alerts", and only when you have any in the last 90 days. They are different things and are never merged. "High heart rate at rest" is Garmin's watch alert, a threshold and not a rhythm measurement. "ECG flagged for AFib" counts ECG recordings that a device (Fitbit Sense or Charge 6, Withings ScanWatch or BPM Core) flagged. It is a count of recordings, not a diagnosis: "If a doctor has not seen these recordings yet, show them to one." With chest pain, fainting or shortness of breath, seek help at once.

When it updates#

• Body Alert, Immunity and Breathing are computed when your night arrives and again with new data. They do not drift through the day. Today's stress is not used until tomorrow.
• If the night has not arrived yet, Body Status scores the day on your usual night and marks it "Provisional" (Body Status).
• Safety alerts are read from the same data and move when a night, a blood-pressure reading or a check-in comes in.
• Results are reused for up to 5 minutes. A past day you open is recalculated from the data we hold for it, so late data or a changed calculation can move it a little.

Free and Premium#

On the free plan (from 1 November 2026) you keep today's Body Status with its verdict, the red flags and the question "How do you feel?", and all safety alerts: a danger reading is never a Premium feature. The cards on the Overview, Health and Sleep tabs (Body Alert, "Signals watched", "How the number is built", Immunity, Breathing, Resilience, Overnight physiology, heart sensor alerts) and past days are Premium. Your data keeps arriving and nothing is lost. Premium includes the 7-day trial (plans).

Energy pacing mode#

The calculations do not change. The mode hides Overtraining, adds the "Crash" answer to the check-in ("A crash today": the day turns to rest and does not count as an illness) and names stress "body load" (energy pacing).

What to do#

• If your Body Alert is high for no reason you can name and you feel unwell: rest, drink, sleep, keep an easy day, and give it a day or two before testing yourself. Check your temperature with a thermometer.
• See a doctor if you feel worse, if it does not ease within a few days, or at once with shortness of breath, chest pain, fainting, confusion, a severe headache, blurred vision or a very high blood pressure.
• Use the check-in. "Ill" and the severity are real inputs.
• Read the whole picture, not one number: open "Signals watched" and "How the number is built" and see which signals moved and for how long.
• Wear the device through the night. Resting heart rate, HRV, breathing and oxygen are all measured then.
• Do not treat a low index as a clean bill of health. It watches what a watch can see and misses what it cannot.
• An alert on blood oxygen, blood pressure or heart rate is worth a conversation with a doctor even when you feel fine.

MyBodyAI is a wellness app, not a medical device. Body Alert, Immunity and Breathing describe signals from your device and do not diagnose. They show signs that often come with an infection or strain, and they also come with ordinary causes. If you feel unwell, see a doctor.

Frequently asked questions#

Does a high Body Alert mean I am getting ill?#

Not by itself. It means several of your signals, such as resting pulse, HRV, breathing, deep sleep or oxygen, have moved away from your usual together. Those are signs that often come with an infection, and they also come with a hard training block, alcohol, a short night, stress or travel. Take it as a reason to rest and watch how you feel, and see a doctor if you feel unwell.

Why is my Body Alert low when I feel ill?#

A cold can start without much change in the signals a watch sees, and it can arrive before the data do. Your own report counts: tap "Ill" in the check-in and the day becomes an Alert, and the index adds points for 3 days.

Why did my Body Alert jump after one night?#

Usually because a floor, a surcharge or a fast move applied: a warm night skin adds 8 or 14, a reported illness 6 to 15, a rapid fall of HRV up to 12, a jump of the resting rate 8. Tap the ring to see each step as a bar of points.

Why does Body Status say Alert but the index is under 55?#

Body Status has more channels than the index (three or more of the "several signals", Overtraining, critically low morning energy, a 3-day pattern of pulse and HRV), accepts your own report, and a danger reading outranks them. Alert needs two independent channels or the same one for a second day (Body Status).

Why is my blood oxygen alert shown when I feel fine?#

A wrist sensor can be wrong, and sleep and altitude lower oxygen. The alert says so and asks you to check it once with a finger oximeter or a doctor. If you have a lower normal, answer the banner and we move the line to your own level (never under 88 %).

Why do I have no Breathing index?#

It needs at least one breathing signal (rate, apnea index, snoring, oxygen or lowest oxygen) from your device. Sleep stages, stress and efficiency alone do not make it. Polar sends no overnight oxygen, for example.

What is the "Several signals at once" box?#

It counts how many separate signals moved together over the last 3 days: resting heart rate, HRV, deep sleep, morning energy, stress, oxygen, a 3-day pattern, a likeness to your earlier illnesses and your own check-in. It appears from 2. It is an estimate of signs of strain and never a diagnosis.

Can I change the limits?#

No. There are no settings for them. A change to a threshold changes every day's number, so we change them only in releases, and these entries are checked against the code each time.