With the Welltory app, you can measure heart rate variability (HRV) using your smartphone camera, heart rate monitor, Apple Watch, or Samsung Watch. Variability measurement is not an electrocardiogram (ECG) recording; it cannot replace an ECG or a doctor's consultation. However, a study published in the scientific journal Elsevier proved that our variability measurement technology is as accurate as ECG monitors.

We use photoplethysmography (PPG), an optical method that measures changes in blood volume within vessels. This technique requires a light source and a photodetector, both conveniently available in a standard smartphone: the flashlight acts as the light source, and the camera serves as the photodetector.

The beating of your heart causes the measured changes. When your heart contracts, the capillaries in your fingertip fill with blood, leading to increased light absorption and darker images. When your heart relaxes, these capillaries contain less blood, resulting in brighter images.

Welltory's advanced algorithms have been trained to detect even the smallest fluctuations precisely. Research supports that this approach is accurate and user-friendly, effectively turning your smartphone into a robust tool for health analysis.

All current iPhone models with a camera and flash are ideal for measurement:

The iPad models are suitable for the measurements:

All modern Samsung models in which the camera and flash are located at a small distance from each other are suitable for measuring. For example:

On some smartphones, the flash is too far from the camera, so it can't illuminate your finger enough during measurement. Such devices include, for example:

You can't take measurements with the camera on these smartphones.

To take an accurate camera measurement:

If your measurements are inaccurate, please read the article «How to take accurate heart rate variability measurements». You will find tips to help you improve the quality of your measurements.

With no external devices connected, camera measurement will be set as default. Otherwise, Welltory will remember the last device you used. To switch back to the camera, head to Menu → Settings → Device or Menu → Settings → Primary Device.

If your phone camera has a green Connected status, it will be used to take measurements.

If your iPhone or iPad has Ultra Wide camera / Back Telephoto camera / Back camera, we recommend switching to it so that the quality of your measurements will be high. To change the camera, please open the app Settings → Measurement Device and select Ultra Wide camera / Back Telephoto camera / Back camera under Phone camera section.

iPhone models where you should choose the Ultra Wide camera:

iPad models where you need to choose the Ultra Wide camera:

iPhone models where you need to choose a camera with the Back Telephoto camera:

iPhone models in which you need to choose the Back camera:

When measuring on iPhone X, your finger should cover the bottom camera and flash. To measure, place your finger parallel to the camera unit, cover the cameras, and flash completely:

When measuring on iPhone 11, your finger should cover the bottom camera and flash. To measure, place your finger diagonally across the camera unit, cover the bottom camera, and flash:

When measuring on iPhone 12, your finger should cover the top camera and flash. To measure, place your finger diagonally across the camera unit, cover the top camera, and flash:

When measuring on iPhone 13, 13mini, 14, and 14 Plus, your finger should cover the top camera and flash. To measure, place your finger perpendicular to the camera unit, cover the top camera, and flash:

When measuring on iPhone 15 and 15 Plus, your finger should cover the bottom camera and flash. To measure, place your finger parallel to the camera unit, cover the bottom camera, and flash:

When measuring on iPhone 16 and 16 Plus, your finger should cover the bottom camera and flash. To measure, place your finger diagonally across the camera unit and completely cover the bottom camera and flash:

When measuring on the iPhone Pro and Pro Max models, your finger should cover the flash and single camera on the right side. To measure, place your finger parallel to the camera unit and cover the camera on the right and the flash:

When measuring on iPad Pro models, your finger should cover the bottom camera and flash. To measure, place your finger diagonally across the camera unit, cover the bottom camera, and flash:

When measuring on the Samsung Galaxy S21 and S21+, your finger should cover the middle camera and flash. To measure, place your finger diagonally across the camera unit, cover the middle camera, and flash:

When measuring on the Samsung Galaxy S21 Ultra, and S22 Ultra, your finger should cover the camera in the middle and the flash. To take a measurement, position your finger diagonally across the camera unit, cover the middle camera, and flash:

On some smartphones, the flash heats up too much and can burn you. In such cases, we recommend keeping your finger 2–3 mm away from it. However, make sure that it continues to touch the camera.

When the measurement starts, you’ll see the image from the relevant camera on your phone’s screen. You're good to go if the screen is bright red (due to the flashlight illuminating your capillaries). If the screen shows your surroundings, your finger is on the wrong camera. Try putting it on each camera one by one until you see a red screen.

Usually, users encounter this issue on Android devices where the cameras and flash are far away from each other. We recommend using a compatible heart rate monitor or Samsung Watch for HRV measurements in such cases.

In the Premium version, users can take unlimited measurements per day. However, you are limited to only one measurement with a camera or heart rate monitor per day in the free version. Once you have taken a measurement using a camera or heart rate monitor, the measurement button in the feed will become locked until 5 a.m. the following day:

The button loader visually indicates the remaining time until you can take another measurement. It automatically updates whenever you open your feed or relaunch the Welltory app.