Measuring HRV with your smartphone

Heart rate variability (HRV) analyzes the variations in time between successive heartbeats. It offers valuable insights into the autonomic nervous system (ANS), helping to reveal how your body responds to stress and recovery. Traditionally, HRV is measured using an electrocardiogram (ECG), which directly captures the heart’s electrical signals, or photoplethysmography (PPG), which detects blood volume changes in peripheral circulation.

But what if you could measure your HRV with nothing more than your smartphone?

Thanks to advances in sensor technology and signal processing, HRV can now be derived from the tiny mechanical movements caused by your heartbeat—using your phone’s built-in accelerometer. In this article, we explain how this works, the science behind it, and how the Kubios HRV mobile app enables resting HRV measurement without needing a separate heart rate sensor.

Kubios Smartphone-based heart rate variability (HRV) measurement

Scientific Background

The idea of detecting cardiac activity through body motion is not new. As early as the late 19th century, Gordon[1] observed heartbeat-induced body movements resulting from the forceful ejection of blood from the heart. As blood travels through the large arteries, it shifts the body’s center of mass, producing recoil forces that cause subtle but detectable micro-movements [2], [3], [4]. Recovery from chronic fatigue takes a much longer period and requires a more sustained approach, focusing on lifestyle changes, stress management, and structured rest periods.

Two scientific measurement approaches enable capturing these subtle movements:

  • Ballistocardiography (BCG): One of the earliest non-invasive cardiac monitoring techniques, BCG measures the body’s recoil forces caused by the heart’s ejection of blood. These signals are typically captured with sensitive accelerometers or sensors embedded in mattresses, chairs, or scales.
  • Seismocardiography (SCG): SCG measures vibrations of the chest wall caused by cardiac mechanical activity. These signals are typically recorded with accelerometers placed on the sternum and are used to study heart contractility, cardiac timing, and respiratory modulation.

With modern sensor technology and smartphones equipped with precise accelerometers, these principles have re-emerged as practical tools for measuring HRV. Kubios builds on these scientific foundations to offer accurate, convenient HRV monitoring through your phone.

Seismocardiography or ballistocardiography, measurement of accelerometer-based heart rate variability (HRV)

Figure: ECG vs. accelerometer-based measurement of cardiac activity.

The Kubios HRV mobile app

The Kubios HRV app brings this innovative technology to your smartphone. With the Readiness Measurement feature, you can now assess your resting HRV simply by placing your phone on your chest while lying down. This method offers a practical and accessible way to track recovery, stress levels, and overall well-being—without needing a chest strap or wearable sensor.

How accelerometer-based HRV measurement works

Each heartbeat generates small mechanical forces that travel through your body. When you lie still and place your smartphone flat on your chest, the phone’s accelerometer can detect subtle chest wall vibrations caused by each heartbeat.

Sophisticated signal processing algorithms convert these vibrations into interbeat interval (IBI) data—the same data used to calculate HRV. For accurate results, it’s important to remain completely still and avoid thick clothing, which could introduce motion artifacts or reduce signal quality. Simply relax and breathe normally throughout the measurement.

With this setup, your smartphone becomes a minimalist HRV sensor, capable of delivering meaningful insights into your physiological state—no chest strap or wearable required.

Taking a Readiness measurement with your smartphone

To ensure reliable results, consistency is key. We recommend the following steps:

  1. Position and timing: Use a consistent body position (reclined or semi-reclined) at a regular time, preferably in the morning upon waking.
  2. Start the measurement: Place your phone flat on your sternum (either on thin clothing or directly on the skin) and relax. The phone should rest naturally—do not hold or touch it during the measurement. The app will automatically begin recording after the relaxation period.
  3. Relax and breathe normally: During the measurement, remain completely still, avoid speaking, and breathe normally. The app will notify you when the measurement is complete.
  4. Check the quality: After the measurement, review the signal quality. If it’s poor, repeat the measurement while ensuring minimal movement and correct phone placement.
Kubios HRV app, taking a readiness measurement

Benefits of accelerometer-based HRV measurements

The benefits of this measurement method include:

  • Convenience: No need for external sensors or chest straps. Your smartphone becomes your HRV monitor.
  • Accessibility: Easily incorporate HRV measurement into your daily routine.
  • Non-Invasive: A comfortable and effortless way to assess your stress-level or heart health.
  • Reliable HRV insights: When used under resting conditions with proper positioning and minimal movement, results are consistent and accurate.

It’s important to use this method only for resting HRV measurement, taken in a quiet environment while lying completely still, as the signal is highly sensitive to motion artifacts. The method is not intended for use during physical activity or high-motion environments. Additionally, the method is optimized for normal resting heart rates, so your heart rate should remain below 90 beats per minute during the measurement to ensure accurate results.

Kubios HRV app, measuring heart rate variability (HRV) with your smartphone

Accuracy of accelerometer-based HRV measurements

Although not as precise as ECG-based measurements, accelerometer-based HRV has shown high reliability under resting conditions. When the phone is properly positioned and the user remains still, the method performs well.

Multiple research studies have confirmed the reliability of this approach. When comparing seismocardiographic measurements with ECG-based recordings, researchers have shown that heart rate can be accurately extracted, and the time intervals between beats—as well as commonly used HRV parameters—can be estimated with good precision [5], [6], [7].

The Kubios HRV app uses a robust beat detection algorithm tailored for accelerometer signals. Combined with our advanced noise detection and validated beat correction, it ensures accurate and reliable HRV data.

Try the future of HRV measurement

With the Kubios HRV mobile app, monitoring your physiological readiness is simpler than ever. Accelerometer-based HRV tracking offers a science-backed, hardware-free way to assess stress and recovery—right from your smartphone.

Whether you’re a health-conscious individual or a coach working with athletes or clients, this method offers a powerful tool for understanding autonomic nervous system balance, recovery, and well-being.

👉 Download the Kubios HRV App and start measuring your resting HRV today—with nothing more than your smartphone and a few minutes of quiet time.

Frequently Asked Question (FAQ)

Is smartphone-based HRV measurement accurate?

Yes. When lying still and placing the smartphone flat on your sternum, accelerometer-based HRV measurement can provide accurate insights for general readiness and wellness monitoring. It offers a convenient and reliable alternative to ECG-based methods—especially for resting conditions.

 

What is the relaxation period?

The relaxation period allows you to calmly lie down and position your phone before the actual measurement begins. It typically lasts at least 30 seconds. After this period, the measurement starts automatically, and the app will notify you when it’s complete. You can adjust the length of the relaxation period in the app settings.

 

What’s the ideal duration for a readiness measurement?

While the readiness measurement can technically be as short as 30–60 seconds, we recommend a 3-minute recording to ensure reliable resting HRV analysis. The measurement can be extended up to 5 minutes if desired, but 3 minutes typically provides a good balance between data accuracy and ease of staying still for the entire duration.

 

What if the signal quality is low?

For optimal signal quality, lie in a relaxed position, wear thin clothing on your upper body, and place your phone flat on your sternum. Do not hold or touch the phone during the measurement—let it rest naturally on your chest. Remain completely still, breathe normally, and avoid any movement or talking. If the signal quality remains low, try adjusting the phone’s position and repeating the measurement.

References 

  1. Gordon JW. Certain molar movements of the human body produced by the circulation of the blood. J Anat Physiol, 11:533–536, 1877.
  2. Inan OT, Migeotte PF, Park KS, Etemadi M, Tavakolian K, Casanella R, Zanetti J, Tank J, Funtova I, Prisk GK, and Di Rienzo M. Ballistocardiography and seismocardiography: a review of recent advances. IEEE J Biomed Health Inform, 19(4):1414-27, 2015.
  3. Taebi A, Solar BE, Bomar AJ, Sandler RH, and Mansy HA. Recent advances in seismocardiography. Vibration, 2(1):64-86, 2019.
  4. Sadek I, Biswas J, and Abdulrazak B. Ballistocardiogram signal processing: a review. Health Inf Syst, 7(1):10, 2019.
  5. Wahlström J, Skog I, Händel P, Khosrow-khavar F, Tavakolian K, Stein PK, and Nehorai A. A hidden Markov model for seismocardiography. IEEE Trans Biomed Eng, 64(10):2361-2372, 2017.
  6. Centracchio J, Parlato S, Esposito D, Bifulco P, and Andreozzi E. ECG-free heartbeat detection in seismocardiography signals via template matching. Sensors, 23, 4684, 2023.
  7. Pustozerov E, Kulau U, and Albrecht U-V. Automated heart rate detection in seismocardiograms using electrocardiogram-based algorithms—A feasibility study. Bioengineering, 11, 596, 2024.