Sensors in the real world

Wearable PPG sensors.

Explore optical sensors across watches, rings, and other wearables. Look closer at design choices, published evidence, and practical limitations.

NewWearable accuracy leaderboards: heart rate, HRV, sleep, SpO2 and AFib from published studies →

Photograph of an Apple Watch Series 10 in jet black aluminum with a black sport band.

Apple Watch PPG Sensor: Technical Deep-Dive

Apple Watch uses reflective optical sensing with green LEDs and photodiodes for heart rate, and can also use infrared light. Models that support Blood Oxygen add red and infrared light for wellness SpO2 estimates. Apple does not publish exact LED wavelengths or detector counts for every generation.

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Photograph of a Garmin fēnix 8 47 mm AMOLED with a slate gray case and a black silicone band.

Garmin Elevate v5 Optical Sensor: PPG Specs and Accuracy

Garmin's Elevate optical sensor uses multiple LEDs and detectors for wrist heart rate, HRV-derived features, and Pulse Ox on supported watches. Garmin does not publish a universal sampling rate, wavelength list or heart-rate accuracy figure for the sensor family, and accuracy varies with model, fit and activity.

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Photograph of a Fitbit Charge 6 with a coral band.

Fitbit PurePulse 2.0: PPG Sensor Deep-Dive

Fitbit introduced PurePulse 2.0 with the Sense and Versa 3 in 2020: a multi-path optical heart-rate sensor with more LED and photodiode paths and an updated algorithm. Fitbit devices use it for heart rate, HRV, SpO2 and sleep features; Fitbit does not publish a numeric heart-rate accuracy specification.

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Photograph of a silver Oura Ring 4, with the inner sensor windows visible.

Oura Ring: Finger PPG Sensor and Accuracy

Oura Ring 4 uses an 18-path PPG system: green and infrared LEDs alternate for heart rate and HRV, and red plus infrared LEDs estimate blood oxygen during sleep. Its finger placement can give a strong resting signal, and ECG-referenced studies report close agreement for nightly average heart rate and HRV.

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Photograph of the Sensor Bio V2 wrist band from Sensor Bio’s product page, full device in view

Sensor Bio V2: B2B Raw PPG Platform

Sensor Bio V2 (model S2001) is a screenless B2B platform: configurable PPG sampling, raw waveform export for enterprise partners, and an SDK on Sensor Bio’s cloud. Sensor Bio describes that export as AI-ready data. It is a general wellness device, not FDA cleared, and not a consumer score app.

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Photograph of a Samsung Galaxy Watch7 in green.

Samsung Galaxy Watch BioActive Sensor

Samsung's BioActive Sensor combines optical PPG, electrical heart (ECG) electrodes and bioelectrical impedance in one module. On Galaxy Watch7, Samsung says the sensor adds blue, yellow, violet and ultraviolet LEDs to a larger number of green, red and infrared LEDs. Blood pressure estimates require calibration against an upper-arm cuff every 28 days.

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WHOOP 4.0: PPG Sensor and Recovery Science

WHOOP 4.0's sensor has 5 LEDs (three green, one red, one infrared) and 4 photodiodes. WHOOP computes HRV as RMSSD during sleep and uses it with resting heart rate, respiratory rate and sleep in its daily Recovery score.

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Photograph of a Polar Vantage V3 in night black.

Polar Heart Rate Sensors: PPG and ECG Accuracy

Polar H10 is an ECG chest strap widely used as a reference for heart rate and RR intervals in wearable validation studies. Polar's own tests found it detected RR intervals within 2 ms of ECG in 95.6% of cases across activities. Polar Vantage watches use wrist PPG, which agrees closely with a chest strap at rest and during sleep but less well at high exercise intensities.

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Photograph of a Google Pixel Watch 3 with a polished silver case and a porcelain band.

Google Pixel Watch 3: Optical Sensor

Pixel Watch 3 uses a multi-path optical heart-rate sensor, red and infrared sensors for SpO2 estimates, ECG-compatible electrical sensors, a cEDA skin-conductance sensor and a skin-temperature sensor. The photograph is the 2024 polished-silver Pixel Watch 3.

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Photograph of an Amazfit T-Rex Ultra.

Amazfit T-Rex Ultra: PPG Sensor

Amazfit’s T-Rex Ultra lists a BioTracker PPG sensor with blood-oxygen support, up to 20 days of typical battery and 10 ATM water resistance. The photograph is the original T-Rex Ultra, not T-Rex Ultra 2.

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Photograph of a Withings ScanWatch 2, 42 mm, with a black dial and black strap.

Withings ScanWatch 2: PPG Sensor

ScanWatch 2 is a hybrid analog watch. Withings lists ECG, SpO2 and temperature tracking, 5 ATM water resistance, and about 30 days per charge. The photograph is the 42 mm black ScanWatch 2.

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Photograph of a COROS PACE 3 with a nylon band.

COROS PACE 3: PPG Sensor

The photograph is a COROS PACE 3 with a nylon band. COROS lists optical heart rate and SpO2, 15 days of regular use, 38 hours of GPS and 5 ATM water resistance for the PACE 3. The VERTIX 2S is a different watch.

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Photograph of a Suunto Race in all black.

Suunto Race: PPG Sensor

The photograph is a Suunto Race in all black. Suunto lists up to 16 days of daily use with heart rate on, waterproofing to 100 m, and a blood-oxygen widget that is not for medical use.

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Photograph of an Ultrahuman Ring PRO in bionic gold, resting on fabric.

Ultrahuman Ring PRO: Finger PPG

The photograph is an Ultrahuman Ring PRO in bionic gold. Ultrahuman also sells Ring AIR. Ultrahuman lists up to 15 days of battery for Ring PRO, 4–6 days for Ring AIR, and 100 m water resistance.

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Product image of a white Empatica EmbracePlus, with a round screen and a perforated band.

Empatica EmbracePlus and E4

Empatica’s current research watch is EmbracePlus. E4, its predecessor, is retired. Both are wrist wearables with PPG, electrodermal activity, temperature and motion sensors. The photograph on this page is EmbracePlus.

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