Short answer: Apple Watch’s Vitals app can flag unusual changes in overnight health measurements before a wearer consciously notices symptoms. But it does not diagnose illness, identify COVID-19 or flu, or reliably predict when someone will become sick.
Reports that appeared in October 2024 described users seeing elevated wrist temperature and other outlying readings for two or three nights before developing symptoms. Those experiences are plausible and useful as anecdotes, but they are not clinical evidence that Vitals can predict sickness.
As an Amazon Associate I earn from qualifying purchases.
What the Vitals app actually does
Vitals, introduced with watchOS 11, summarizes several overnight measurements and compares them with your personal typical range. Depending on your Apple Watch model and region, it can show:
- Heart rate
- Respiratory rate
- Wrist temperature
- Blood oxygen, where supported
- Sleep duration
The important detail is that Vitals generally compares you with yourself, not with one universal “healthy” number. Apple says its typical ranges are based on your historical information. The algorithm was also developed using real-world data from the Apple Heart and Movement Study.
#1 Best Overall
![Apple Watch Series 11 [GPS 46mm] Smartwatch with Jet Black Aluminum Case with Black Sport Band - M/L. Sleep Score, Fitness Tracker, Health Monitoring, Always-On Display, Water Resistant](https://m.media-amazon.com/images/I/416RQ0rtsUL._SL160_.jpg)
- A FULL-FEATURED HEALTH TRACKER—Apple Watch Series 11 gives you invaluable insights about your body, right from your wrist. Take an ECG anytime* and get alerts for a high and low heart rate or an irregular rhythm*—so you can stay closer to your heart. You can also view your overnight health tracking metrics with the Vitals app* and be notified of possible sleep apnea.*
- KNOW YOUR SLEEP SCORE—With advanced sleep tracking, Series 11 gives you a daily sleep score. It’s an easy way to help measure and understand the quality of your sleep, so you can make it more restorative.
- GET HYPERTENSION NOTIFICATIONS—Did you know that Series 11 can spot signs of chronic high blood pressure? By analyzing how your blood vessels respond to beats of the heart, it can notify you of possible hypertension.*
- SAFETY FEATURES—A smartwatch that puts your safety first. Series 11 can detect a hard fall or severe car crash, automatically help connect you with emergency services, and notify your emergency contacts.* Check In can automatically notify a loved one when you’ve arrived at your destination.
- A POWERFUL FITNESS TRACKER—With advanced metrics and motivating features like Pacer, Heart Rate Zones, training load, and Workout Buddy powered by Apple Intelligence from your nearby iPhone*—Series 11 is made to help everyone stay active, from runners and hikers to strength-training enthusiasts.
That makes the app useful for spotting change, but it also limits what an alert can tell you. A measurement that is unusual for you may be normal for someone else, while a result that remains inside your typical range does not prove that you are healthy.
What a Vitals alert means
When multiple tracked metrics fall outside your typical range, Vitals can notify you and offer possible context. Apple lists factors such as medication, changes in elevation, alcohol and illness.
That notification should be read as:
“Several of your overnight measurements are different from usual.”
The Tool Desk
Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Special offer. See more information about Outbyte and uninstall instructions. Please review EULA and Privacy policy.
It should not be read as:
- “You have the flu.”
- “You have COVID-19.”
- “You are contagious.”
- “You need antibiotics.”
- “A medical emergency is occurring.”
Apple explicitly says that Vitals measurements are not intended for medical use. The app may help you notice that something has changed; it does not identify the cause.
Why people describe it as predicting sickness
The October 2024 reports came largely from Reddit posts discussed by MacRumors, AppleInsider and Android Authority.
Rank #2
![Apple Watch Series 11 [GPS 42mm] Smartwatch with Rose Gold Aluminum Case with Light Blush Sport Band - S/M. Sleep Score, Fitness Tracker, Health Monitoring, Always-On Display, Water Resistant](https://m.media-amazon.com/images/I/31caPPnRysL._SL160_.jpg)
- A FULL-FEATURED HEALTH TRACKER—Apple Watch Series 11 gives you invaluable insights about your body, right from your wrist. Take an ECG anytime* and get alerts for a high and low heart rate or an irregular rhythm*—so you can stay closer to your heart. You can also view your overnight health tracking metrics with the Vitals app* and be notified of possible sleep apnea.*
- KNOW YOUR SLEEP SCORE—With advanced sleep tracking, Series 11 gives you a daily sleep score. It’s an easy way to help measure and understand the quality of your sleep, so you can make it more restorative.
- GET HYPERTENSION NOTIFICATIONS—Did you know that Series 11 can spot signs of chronic high blood pressure? By analyzing how your blood vessels respond to beats of the heart, it can notify you of possible hypertension.*
- SAFETY FEATURES—A smartwatch that puts your safety first. Series 11 can detect a hard fall or severe car crash, automatically help connect you with emergency services, and notify your emergency contacts.* Check In can automatically notify a loved one when you’ve arrived at your destination.
- A POWERFUL FITNESS TRACKER—With advanced metrics and motivating features like Pacer, Heart Rate Zones, training load, and Workout Buddy powered by Apple Intelligence from your nearby iPhone*—Series 11 is made to help everyone stay active, from runners and hikers to strength-training enthusiasts.
One user said Vitals showed three nights of high wrist-temperature outliers before they realized they were ill. Other users described similar experiences, including advance warnings on more than one occasion. Some accounts were less dramatic: the watch displayed unusual readings, but the wearer did not interpret them as a prediction until symptoms appeared.
These stories establish three things for the people who experienced them:
Quick wins for a faster PC:
Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →- The watch detected measurements that differed from their normal pattern.
- The changes preceded symptoms.
- The users later connected the two events.
They do not establish that Vitals identified a pathogen, diagnosed an illness or provides a dependable two- or three-day warning. The reports are self-selected anecdotes, not a controlled study measuring sensitivity, specificity, false positives or false negatives.
Why illness might change overnight readings
Illness can affect several measurements that Vitals tracks. Resting heart rate may rise, respiratory rate may change, sleep may become shorter or more disrupted, and wrist temperature may move higher than its usual overnight level. Blood oxygen can also change in some circumstances.
That physiological logic explains why an illness-related pattern is possible. It does not make any individual measurement specific to infection. The same changes can follow a hard workout, poor sleep, stress, alcohol, travel, altitude exposure, medication or other ordinary events. Menstrual-cycle changes, environmental temperature and sensor fit may also affect what the watch records.
Rank #3
![Apple Watch SE 3 [GPS 40mm] Smartwatch with Starlight Aluminum Case with Starlight Sport Band - S/M. Fitness and Sleep Trackers, Heart Rate Monitor, Always-On Display, Water Resistant](https://m.media-amazon.com/images/I/31YiTby0pOL._SL160_.jpg)
- GET SMARTER HEALTH INSIGHTS—Apple Watch SE 3 is an advanced health tracker that helps you better understand your body. The smartwatch sends alerts for an irregular heart rhythm, or an unusually high or low heart rate.* You can view your overnight health tracking metrics with the Vitals app,* track your sleep score, and get sleep apnea notifications.*
- A GREAT FITNESS TRACKER—SE 3 can track your workouts in a healthy number of ways—from running and strength training to simply achieving your 10K steps a day. With real-time metrics and Workout Buddy powered by Apple Intelligence from your nearby iPhone,* you’ll hit your goals like never before.
- KEEP HELP CLOSE AT HAND—SE 3 is a smartwatch that can detect a hard fall or severe car crash and automatically help connect you to emergency services and notify your emergency contacts.* Check In can automatically notify a loved one when you’ve arrived at your destination.
- WOMEN’S HEALTH INSIGHTS—SE 3 has advanced sensors that track your wrist temperature while you sleep. With this smartwatch, you can log your periods and symptoms, get period predictions, and get notified of cycle deviations.*
- GREAT BATTERY LIFE AND FASTER CHARGING—Enjoy a smartwatch with all-day, 18-hour battery life* from sunup to sundown. Then charge up to twice as fast as SE 2* and get up to 8 hours of battery in just 15 minutes.*
Wrist temperature deserves particular caution. It is a relative overnight measurement compared with your baseline, not the same thing as a conventional oral, ear, forehead or core-temperature reading. A higher-than-usual wrist temperature does not automatically mean you have a fever.
Crashes, No Sound, or Screen Glitches?
Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteWindows Errors? Fix Them Before They Spread
Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallHow to check your readings
On Apple Watch
- Open the Vitals app.
- Turn the Digital Crown to review overnight metrics.
- Tap a metric for more detail.
- Tap the calendar icon in the upper-left corner to review the previous seven days.
- Tap Overnight Vitals, then More Info, to see Apple’s explanation of outliers and possible contributing factors.
On iPhone
- Open the Health app.
- Tap Search, then Vitals.
- Use the daily, weekly, monthly or six-month views.
- Tap Show More Vitals Data to inspect categories, outlier counts and high, typical or low states.
The app’s history is organized around seven-day, monthly and six-month views. You should wear the watch overnight for several nights while it builds a personal baseline, but the existence of a seven-day display should not be confused with seven days of medically validated illness-prediction data.
Why Vitals can miss illness—or raise a false alarm
Vitals is less useful when the watch has little or no overnight data. Practical limitations include charging the watch during sleep, wearing the band too loosely, having an incomplete or unstable baseline, or experiencing an illness that does not noticeably change the tracked measurements.
An outlier may also have nothing to do with sickness. Possible explanations include:
- Alcohol or medication
- Altitude or travel
- Stress or unusually poor sleep
- Hard exercise and recovery
- Environmental changes
- Menstrual-cycle-related changes
- A watch that moved or did not maintain good skin contact
There is another interpretive problem: people are more likely to remember an alert that seemed to come true than an alert that led nowhere. That makes personal success stories compelling, but it cannot provide a general accuracy rate for all Apple Watch users.
Recommended Free Tools
Rank #4
![Apple Watch SE 3 [GPS 40mm] Smartwatch with Midnight Aluminum Case with Midnight Sport Band - S/M. Fitness and Sleep Trackers, Heart Rate Monitor, Always-On Display, Water Resistant](https://m.media-amazon.com/images/I/31Gq8SToFJL._SL160_.jpg)
- GET SMARTER HEALTH INSIGHTS—Apple Watch SE 3 is an advanced health tracker that helps you better understand your body. The smartwatch sends alerts for an irregular heart rhythm, or an unusually high or low heart rate.* You can view your overnight health tracking metrics with the Vitals app,* track your sleep score, and get sleep apnea notifications.*
- A GREAT FITNESS TRACKER—SE 3 can track your workouts in a healthy number of ways—from running and strength training to simply achieving your 10K steps a day. With real-time metrics and Workout Buddy powered by Apple Intelligence from your nearby iPhone,* you’ll hit your goals like never before.
- KEEP HELP CLOSE AT HAND—SE 3 is a smartwatch that can detect a hard fall or severe car crash and automatically help connect you to emergency services and notify your emergency contacts.* Check In can automatically notify a loved one when you’ve arrived at your destination.
- WOMEN’S HEALTH INSIGHTS—SE 3 has advanced sensors that track your wrist temperature while you sleep. With this smartwatch, you can log your periods and symptoms, get period predictions, and get notified of cycle deviations.*
- GREAT BATTERY LIFE AND FASTER CHARGING—Enjoy a smartwatch with all-day, 18-hour battery life* from sunup to sundown. Then charge up to twice as fast as SE 2* and get up to 8 hours of battery in just 15 minutes.*
Compatibility and sensor limitations
The Vitals app requires watchOS 11 or later and iOS 18 or later. Not every metric is available on every Apple Watch model or in every region.
Apple says wrist-temperature sensing is available on Apple Watch Series 8 or later and on any Apple Watch Ultra model. Older watches may still provide other supported metrics, but they will not offer the wrist-temperature readings central to some of the illness anecdotes.
Blood Oxygen is especially complicated in the United States. Apple says it is not supported on Apple Watch SE. On affected Apple Watch models purchased in the U.S. on or after January 18, 2024, with part numbers ending in LW/A, blood-oxygen analysis is performed on the paired iPhone, and Blood Oxygen data is not available in the Vitals app. Do not assume that every U.S.-sold Apple Watch contributes blood-oxygen data.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Can Vitals replace medical testing?
No. Use Vitals as a prompt to pay attention, not as a diagnostic instrument.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
If you feel unwell, a conventional thermometer, an appropriate pulse oximeter, an approved test or advice from a healthcare professional may be more directly relevant. Do not use a Vitals alert to adjust medication, decide that you are safe to work around other people, rule out an infection or determine whether emergency care is necessary. Seek urgent medical help for serious or rapidly worsening symptoms regardless of what the app says.
Best Value
![Apple Watch Series 11 [GPS 42mm] Smartwatch with Jet Black Aluminum Case with Black Sport Band - S/M. Sleep Score, Fitness Tracker, Health Monitoring, Always-On Display, Water Resistant](https://m.media-amazon.com/images/I/41s72HIk5TL._SL160_.jpg)
- A FULL-FEATURED HEALTH TRACKER—Apple Watch Series 11 gives you invaluable insights about your body, right from your wrist. Take an ECG anytime* and get alerts for a high and low heart rate or an irregular rhythm*—so you can stay closer to your heart. You can also view your overnight health tracking metrics with the Vitals app* and be notified of possible sleep apnea.*
- KNOW YOUR SLEEP SCORE—With advanced sleep tracking, Series 11 gives you a daily sleep score. It’s an easy way to help measure and understand the quality of your sleep, so you can make it more restorative.
- GET HYPERTENSION NOTIFICATIONS—Did you know that Series 11 can spot signs of chronic high blood pressure? By analyzing how your blood vessels respond to beats of the heart, it can notify you of possible hypertension.*
- SAFETY FEATURES—A smartwatch that puts your safety first. Series 11 can detect a hard fall or severe car crash, automatically help connect you with emergency services, and notify your emergency contacts.* Check In can automatically notify a loved one when you’ve arrived at your destination.
- A POWERFUL FITNESS TRACKER—With advanced metrics and motivating features like Pacer, Heart Rate Zones, training load, and Workout Buddy powered by Apple Intelligence from your nearby iPhone*—Series 11 is made to help everyone stay active, from runners and hikers to strength-training enthusiasts.
Vitals also sits alongside, rather than replaces, Apple’s other health features. Heart-rate notifications address unusually high or low heart rate; ECG records a single-lead electrocardiogram for supported rhythm assessments; sleep-apnea notifications look for possible breathing disturbances during sleep; and hypertension notifications are designed for a separate pattern associated with chronic high blood pressure. None turns Vitals into a general illness detector. Apple describes the broader feature set on its Apple Watch Series 11 page and in its health-feature documentation.
Is an Apple Watch worth buying for illness warnings?
Not if illness detection is the main reason. There is no cited clinical evidence that Vitals reliably predicts flu, COVID-19 or another specific infection, and Apple does not market it as a medical diagnostic tool.
It may be a useful secondary benefit if you already want overnight sleep tracking, activity data, heart-rate monitoring and Apple’s safety features. Vitals does not require a separate subscription, and its personal-trend approach can help some wearers notice that a night was unusual.
Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsFor buyers considering Apple’s current lineup:
- Budget-focused: The current Apple Watch SE is the logical starting point if Vitals, sleep tracking and basic heart-rate features are the priority. It lacks some higher-end hardware, including ECG and Blood Oxygen.
- Broader health features: Series 11 adds a wider set of health capabilities and is the more appropriate choice for buyers who want ECG and broader sensor coverage. Apple launched it in the U.S. from $399 in September 2025; current pricing should be checked on the Apple Store.
- Outdoor and premium features: Ultra 3 includes Vitals, but its larger case, weight and adventure-focused features make it difficult to justify for illness tracking alone.
Apple Watch requires an iPhone. Apple’s current shopping pages state that the latest models require an iPhone 11 or later running iOS 26 or later. None of the models provides a conventional fever measurement or a clinically validated infection forecast.
Quick Recap
The evidence in one view
| Claim | What the evidence supports |
|---|---|
| Vitals tracks overnight health data | Strong: documented by Apple. |
| Illness can be one reason readings change | Strong: Apple lists illness among possible contributing factors. |
| Some users noticed changes before symptoms | Moderate: reported by multiple technology publications from user anecdotes. |
| Vitals predicts sickness two or three days ahead | Weak: some users reported this, but it is not a general performance claim. |
| Vitals identifies COVID-19, flu or another disease | Unsupported by the cited evidence. |
| Vitals is a medical diagnostic tool | Contradicted by Apple’s medical-use disclaimer. |
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
