We took apart the specs of every major wearable, sensor by sensor and metric by metric. Exactly what hardware you are paying for, what health data it produces, and which features are only software.
Where the difference lives
software > hardware
Sensors
16
Physical hardware
Algorithms
25
Proprietary software
Across 6 latest-generation devices · brands share sensors, not the maths on top
Apple Watch SpO2 in the US: Blood oxygen was disabled Jan 2024 (Masimo patent). Re-enabled Aug 2025 via iPhone-processed workaround. Masimo is contesting. Works normally outside the US.
Metric
Sensor
Garmin
Whoop
Oura
Apple S10
Apple Ultra 3
Fitbit
Resting Heart Rate
PPG
24/7
24/7, 26 Hz
24/7, 18-path
24/7
24/7
24/7
Heart Rate Variability
PPG
Trends + status
Nightly avg
Nightly + daytime
Nightly avg
Nightly avg
Nightly avg
ECG / AFib Detection
ECG electrodes
On-demand + alerts
MG only
No ECG
On-demand + alerts
On-demand + alerts
On-demand + Irregular Rhythm
Blood Oxygen (SpO2)
Red + IR LEDs
On-demand + overnight
Continuous overnight
Overnight auto
On-demand + background
On-demand + background
Overnight
Respiratory Rate
PPG + Accel
Sleep
24/7
Sleep
Sleep
Sleep
Sleep
Skin Temp Trends
Temp sensor
Deviation
Deviation
Deviation
Sleep only
Sleep only
Variation
Sleep Apnea
Accelerometer
FDA-authorized
FDA-authorized
Hypertension Alerts
PPG (pulse wave)
Series 11 only
30-day trend alerts
Stress (Direct)
EDA sensor
EDA + HRV combined
Stress (HRV-derived)
PPG → HRV
Stress Score
Stress metric
Daytime Stress
Also uses HRV
Elevation / Floors
Barometric altimeter
Yes
Yes
Yes
Fall / Crash Detection
Accel + Gyro
Yes
Yes
Yes
Dive Depth
Depth gauge
Up to 6m
Up to 40m
Cycle / Menstrual
Temp + PPG
Temp-based
Temp + HRV
Temp-based
Wrist temp
Wrist temp
Basic tracking
Hearing Health
Microphone
Noise exposure alerts
Noise exposure alerts
Water Temperature
Depth/temp gauge
In swim workouts
In swim workouts
Garmin
6 algorithms
Body Battery
Inputs: HRV + stress + sleep + activity
0–100 energy score. Charges during rest, drains with activity/stress. Real-time updates.
Only score showing live energy drain throughout the day. Built with Firstbeat Analytics.
Training Readiness
Inputs: HRV + sleep + recovery + multi-day load
Tells you if your body can handle a hard workout today.
Factors in training load across multiple days, not just last night's sleep.
HRV Status
Inputs: Overnight HRV over weeks
Shows your HRV baseline trend: balanced, low, or improving.
Long-term trend view rather than a single nightly number.
Health Status
Inputs: HR + HRV + sleep + SpO2 + resp rate
Integrates 5 key health metrics into one view.
New to Venu 4. Quick daily health check-in.
Sleep Coach
Inputs: Sleep data + circadian rhythm
Personalized sleep schedule suggestions with consistency scores.
Tracks sleep regularity and circadian alignment.
Lifestyle Habit Logging
Inputs: User-logged behaviors (40+)
Log daily habits and see how they correlate with Body Battery, sleep, and stress.
Similar to Whoop Journal but with 40+ trackable habits.
Whoop
8 algorithms
Recovery Score
Inputs: HRV + RHR + resp rate + sleep
0–100% morning score. Green / yellow / red.
Core feature. Tuned for strain-to-recovery balance.
Strain Score
Inputs: HR during activity
0–21 scale of cardiovascular load.
Measures daily cardiovascular load paired with Recovery.
VO2 Max
Inputs: HR + activity data
Estimates cardiovascular fitness from heart rate and exercise.
Added in 2025. Linked to Healthspan as a longevity indicator.
Healthspan / Whoop Age
Inputs: 9 metrics including HRV, RHR, sleep, temp
Estimates biological age and "Pace of Aging."
Only device with a longevity metric. Built with Buck Institute.
Hormonal Insights
Inputs: Temp + HRV + sleep + cycle data
Shows how menstrual cycle phases affect recovery and sleep.
Correlates hormonal phases with performance data.
Journal
Inputs: User-logged behaviors (160+)
Tracks daily habits and correlates them with recovery/sleep.
Most extensive behavior tracking: 160+ habits.
Sleep Coach / Planner
Inputs: Sleep data + circadian rhythm
Recommends optimal bedtime. Haptic alarm at ideal wake time.
Personalized sleep scheduling with vibration-based wake-up.
Whoop Coach (AI)
Inputs: All biometric data
AI assistant answering natural-language health questions.
Only device with a conversational AI coach (powered by OpenAI).
Oura
4 algorithms
Readiness Score
Inputs: Temp + HRV + RHR + sleep + activity
Daily score: how prepared your body is.
Benefits from finger-based signal. Leans on temp deviations.
Cardiovascular Age
Inputs: RHR + HRV + VO2 Max + age
Estimates your heart's biological age.
Paired with Cardio Capacity. Oura-only metric.
Cardio Capacity (VO2 Max)
Inputs: Accel + PPG during walking test
Estimates VO2 Max from a guided walking test.
Requires manual walking test to calibrate.
Resilience
Inputs: HRV + sleep + activity + stress
Long-term score of stress-recovery patterns.
Tracks recovery patterns over weeks/months. Oura Labs.
Apple
4 algorithms
Sleep Score
Inputs: Accel + PPG + temp
Rates overall sleep quality.
Newer feature: less mature than Oura or Whoop sleep algorithms.
Vitals App
Inputs: HR + resp rate + temp + SpO2 + sleep
Dashboard of overnight health metrics with alerts.
Consolidates multiple sensors into one daily health view.
Cardio Fitness (VO2 Max)
Inputs: GPS + accel + PPG
Estimates VO2 Max from outdoor walks/runs.
Passive: calculates automatically. Requires GPS.
Hearing Health
Inputs: Microphone
Monitors noise levels. Alerts when exposure could damage hearing.
Only wearable with hearing protection alerts.
Fitbit
3 algorithms
Daily Readiness
Inputs: HRV + RHR + sleep + activity
1–100 score: push hard or rest.
Requires Fitbit Premium ($9.99/mo) for full insights.
Only score using hardware stress sensor (EDA) alongside HRV.
Active Zone Minutes
Inputs: PPG (HR zones)
Double credit for time in cardio/peak HR zones.
Simpler alternative to Whoop Strain or Garmin Training Load.
Why the Hardware Differences Matter
Same metric name doesn't mean the same measurement. Here's how hardware design affects what you actually get.
Heart Rate & HRV
Oura's 18-path PPG on the finger reads through thinner skin with less motion noise: 31% fewer nighttime gaps vs Gen 3. Whoop counters with 26 Hz sampling (fastest here) for better exercise tracking. Garmin's Elevate Gen 5 added red + IR LEDs alongside green for better accuracy across skin tones.
SpO2 (Blood Oxygen)
All six use red + IR light, but Oura's finger placement and 18-path design gets 120% better signal quality than Gen 3. Whoop runs continuous overnight SpO2. Everyone else does periodic or on-demand checks.
Sleep Apnea
Only Apple Watch (S10, Ultra 3). Uses the accelerometer, not SpO2: detects tiny wrist movements from interrupted breathing. Needs 30 nights of data. 89% accurate for severe apnea, 43% for moderate. FDA-authorized.
Stress Measurement
Fitbit is the only device with a dedicated stress sensor (EDA) that reads sweat gland activity via skin conductance, a direct nervous system signal. Requires 90-sec manual scan. Garmin, Whoop, and Oura estimate stress from HRV (indirect). Apple has no stress feature.
Hypertension
Only Apple Watch Ultra 3. Analyzes how blood vessels respond to heartbeats via PPG. Does NOT give BP numbers; flags 30-day trends. Algorithm trained on 100,000+ participants.
Fall Detection
Garmin and both Apple Watches use accelerometer + gyroscope; the gyro adds rotational data to tell real falls from arm drops. Whoop and Oura lack gyroscopes so can't do this.
Keep exploring
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Oura
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Fitbit
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FDA-Cleared Medical Features
Apple Watch Ultra 3
ECG/AFib, Sleep Apnea, Hypertension
Apple Watch S10
ECG/AFib, Sleep Apnea
Garmin Venu 4
ECG/AFib
Fitbit Charge 6
ECG/AFib
Whoop 5.0
None (MG has ECG)
Oura Ring 4
None
Common questions
Which wearable has the most sensors?
Apple Watch Ultra 3 has the most sensors at 11, followed by Garmin Venu 4 and Apple Watch S10 at 10 each. Whoop 5.0 and Oura Ring 4 have 4 sensors each.
Which wearable has the most FDA-cleared features?
Apple Watch Ultra 3 leads with 3 FDA-cleared features (ECG/AFib, Sleep Apnea, Hypertension). Apple Watch S10 has 2 (ECG, Apnea). Garmin and Fitbit each have 1 (ECG/AFib). Whoop and Oura have none.
What is the difference between hardware and software features on wearables?
Hardware features are physical sensors (PPG, ECG, accelerometer, EDA) that collect raw biometric data. Software features are proprietary algorithms (Body Battery, Recovery Score, Readiness Score) that process sensor data into actionable health insights. The same sensor can produce very different results depending on the algorithm.
Which wearable is best for stress tracking?
Fitbit Charge 6 is the only device with a dedicated EDA (electrodermal activity) stress sensor that measures sweat gland activity, a direct nervous system signal. Garmin, Whoop, and Oura estimate stress indirectly from HRV. Apple Watch has no stress feature.
Which wearable has the best heart rate sensor?
It depends on when heart rate is measured. In independent studies, Apple Watch is the most accurate during exercise, followed by Garmin and Fitbit. Oura Ring 4 is the most accurate overnight at rest, for resting heart rate and HRV, reading from an 18-path PPG sensor on the finger. Whoop 5.0 has the fastest sampling rate at 26 Hz.
Sources
All data from official manufacturer specs, support docs, and independent reviews. Verified March 2026.
Garmin Venu 4
Garmin Newsroom: Venu 4 Announcement
garmin.com
Garmin Venu 4
DC Rainmaker: Venu 4 Hands-On
dcrainmaker.com
Garmin Venu 4
The5kRunner: Elevate Gen 5 Sensor Details
the5krunner.com
Garmin Venu 4
Garmin Wiki: Venu 4 Full Specs
wiki.garminrumors.com
Whoop 5.0
Whoop Press Release: Whoop 5.0 and MG
whoop.com
Whoop 5.0
Whoop Blog: Everything Launched in 2025
whoop.com
Whoop 5.0
Whoop: AI Coach (OpenAI)
whoop.com
Whoop 5.0
The5kRunner: Whoop 4.0 vs 5.0 Architecture
the5krunner.com
Oura Ring 4
Oura Support: Ring 4 Specs
support.ouraring.com
Oura Ring 4
Oura Blog: Technology in Ring 4
ouraring.com
Oura Ring 4
Oura Blog: Smart Sensing (18-path)
ouraring.com
Oura Ring 4
DC Rainmaker: Oura 4 What's Changed
dcrainmaker.com
Apple Watch
Apple Newsroom: Apple Watch Ultra 3
apple.com
Apple Watch
Apple Support: Sleep Apnea Notifications
support.apple.com
Apple Watch
9to5Mac: Accelerometer-Based Sleep Apnea
9to5mac.com
Apple Watch
Apple Newsroom: Blood Oxygen Update (Aug 2025)
apple.com
Apple Watch
Cardiovascular Business: Ultra 3 Hypertension
cardiovascularbusiness.com
Fitbit Charge 6
Google Blog: Introducing Charge 6
blog.google
Fitbit Charge 6
DC Rainmaker: Charge 6 In-Depth Review
dcrainmaker.com
Fitbit Charge 6
Fitbit Support: ECG App
support.google.com
Fitbit Charge 6
Fitbit: Stress Management Technology
fitbit.com
Show all 21 sources
From the blog
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This content is for informational purposes only and is not medical advice. Always consult a qualified healthcare provider before making health decisions based on wearable data.
Data sourced from official manufacturer specs, support documentation, and independent reviews. Last updated October 25, 2026.
As an Amazon Associate, Kygo Health earns from qualifying purchases. Product links on this page are affiliate links; we may earn a commission at no extra cost to you.
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About this hardware and software comparison tool
This free tool shows what actually makes Garmin, WHOOP, Oura, the Apple Watch, and Fitbit different, comparing their hardware sensors, health metrics, and proprietary software side by side. No signup required.
It is built by Kygo Health. Kygo Health is an iOS and Android app that connects AI food logging to wearable data and shows how what you eat affects your sleep, HRV, resting heart rate, energy, and recovery. It syncs Oura Ring, Apple Health, Health Connect, Fitbit, Garmin, and WHOOP. Food logging, wearable syncing, and nutrition tracking are free, including your first 5 AI photo logs. Pro, which unlocks the correlation engine, costs $9.99 per month, $49.99 per year with a 7 day free trial, or $99.99 once for lifetime access. Kygo is a general wellness product, not a medical device.