A dual ECG system

Two electrodes instead of a single optical sensor. That's the difference between “estimating heart rate from light” and recording the heart's real electrical signal.

98%ECG accuracy
500 Hzsignal rate
30–40%PPG accuracy loss

ECG vs. optics

WITU · ECG

An electrical signal

The electrodes read the heart's electrical activity directly. That lets the app capture the signal's shape and flag irregular-rhythm patterns as wellness insights.

Accuracy under load
Flags rhythm irregularities
Accurate HRV (R-R intervals)

Whoop · Oura · optics

Reflected light (PPG)

An LED illuminates the capillaries and the sensor estimates the pulse wave. Convenient for background tracking, but sensitive to motion, skin tone, and blood flow.

−30–40% during motion
Misses rhythm irregularities
HRV error

Two electrodes — one circuit

Electrode on the body

Sits against the skin of the wrist at all times and captures the baseline signal 24/7.

Electrode on the clasp

A second contact point. A touch from the finger of your other hand closes the electrical circuit.

ECG in 30 seconds

A single-lead trace is recorded, and the algorithm flags up to 12 kinds of rhythm irregularity as wellness insights.

DCI — how much you can trust the data

Inaccurate data leads to inaccurate advice. DCI shows how reliable the conclusions are right now.

DCI = sensor accuracy × 0.4 + blood tests × 0.3 + duration × 0.3

40%Sensor accuracyECG vs. optics

30%Blood testsbiochemical context

30%Durationhistory of observations

A user with an optical watch starts at DCI ≈ 60%. By adding ECG measurements and uploading blood tests, they bring the index up to 100% — and only then do the recommendations become truly personal.

About the technology

Why is ECG more accurate than optical heart rate?

ECG records the heart's electrical signal directly through electrodes. Optics (PPG) estimate the pulse wave from reflected light and lose up to 30–40% accuracy during motion. For HRV trends and rhythm-pattern insights, that difference is decisive.

What is DCI?

The Data Confidence Index. It combines sensor accuracy (40%), the presence of blood tests (30%), and the length of observation (30%). The higher the DCI, the more accurate your personal recommendations.

Do I need to press anything for an ECG?

Core metrics are captured automatically 24/7. For a full ECG, just touch the clasp with the finger of your other hand for 30 seconds — the circuit closes and a cardiogram is recorded.

What is the sampling rate?

The ECG channel runs at 500 Hz — enough resolution to read the signal's shape and rhythm patterns, not just heart rate.

References

Claims about ECG vs. optical accuracy rest on peer-reviewed research.

Bent B. et al. Investigating sources of inaccuracy in wearable optical heart rate sensors. npj Digital Medicine, 2020.
Schäfer A., Vagedes J. How accurate is pulse rate variability as an estimate of heart rate variability? International Journal of Cardiology, 2013.

Deeper into the science

See how the dual-ECG system translates into real health insights, or explore WITU's scientific basis.

Explore health Scientific basis

WITU is a wellness device, not a medical device

Insights are provided for general wellness and informational purposes only and are not intended to diagnose, treat, or replace professional medical advice. If you have any health concerns, consult a qualified healthcare provider.