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Measuring heart rate variability
Taking measurements with your smartphone camera
Taking measurements with your smartphone camera
Mark avatar
Written by Mark
Updated over a week ago

In Welltory, you can take measurements of heart rate variability (HRV) with your smartphone camera, a heart rate monitor, or Apple Watch. Note that HRV measurement is not an electrocardiogram (ECG) recording, and it can't be used as a substitute for ECG or a medical check-up.

However, Welltory's HRV measurement accuracy is on par with ECG monitors, according to the results of this study published by Elsevier.

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

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

To take an accurate camera measurement:

  • Make sure your phone has a flashlight.

  • Put your finger so that it covers both the camera and the flashlight.

  • Don’t press too tightly.

  • Don’t move your finger. Our algorithm analyzes the images it gets from the camera. Any movements can distort them.

  • Always use the same finger of the same hand.

Learn more on how to take an accurate measurement.

Note: With some phones, the flashlight may get too hot and even burn. If so, hold your finger 2–3 mm away from it. Make sure your finger still covers the camera.

How it works

We use an optical method called photoplethysmography (PPG). It measures changes in the volume of blood in vessels with a light source and a photodetector.

These changes are caused by the beating of your heart. We detect them by illuminating your finger with a flashlight and measuring the amount of light absorbed using camera images.

When your heart contracts, capillaries in your fingertip are full of blood — more light is absorbed, and the image becomes darker. When your heart expands, there is less blood in your capillaries — less light is absorbed, and the image becomes brighter. Capturing these changes, our algorithm can analyze your heart rate.

Learn more on photoplethysmography.

My smartphone has multiple cameras. How do I know my finger is on the right one?

When the measurement starts, you’ll see the image from the relevant camera on your phone’s screen. If the screen is bright red (due to the flashlight illuminating your capillaries), you’re good to go. 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.

How to take measurements with iPhone X

Your finger should cover the bottom camera and the flashlight as shown below:

How to take measurements with iPhone devices featuring the Ultra Wide camera

The following range of iPhone devices has the Ultra Wide camera:

  • iPhone 11

  • iPhone 11 Pro

  • iPhone 11 Pro Max

  • iPhone 12

  • iPhone 12 mini

  • iPhone 12 Pro

  • iPhone 12 Pro Max

  • iPhone 13

  • iPhone 13 mini

  • iPhone 13 Pro

  • iPhone 13 Pro Max

  • iPhone 14

  • iPhone 14 Plus

  • iPhone 14 Pro

  • iPhone 14 Pro Max

If you own one of the devices listed above, we recommend you to switch to the Ultra Wide camera to improve the quality of your measurements. To change the camera, please open the app Settings → Measurement Device and select Ultra Wide camera under the Phone camera section.

The pictures below illustrate how your finger should cover the camera and the flash when you take a measurement with the iPhone devices featuring the Ultra Wide camera.

  • Finger positions for measurements with iPhone 11:

  • Finger positions for measurements with iPhone 12 and iPhone 12 mini:

  • Finger positions for measurements with iPhone 11 Pro, iPhone 12 Pro, iPhone 13 Pro, iPhone 14 Pro, iPhone 11 Pro Max, iPhone 12 Pro Max, iPhone 13 Pro Max, and iPhone 14 Pro Max:

  • Finger positions for measurements with iPhone 13, iPhone 13 mini, iPhone 14, and iPhone 14 Plus:

How to take measurements with Samsung Galaxy S21 +

Your finger should cover the Wide camera in the middle and the flash:

How can I take a measurement if the flash is placed too far from the camera and can't illuminate my finger?

Some smartphones are equipped with the flash placed too far from the camera, so it can't light the finger enough when you take a measurement. Such devices include, for example:

  • Google Pixel 6

  • Google Pixel 6A

  • Google Pixel 6 Pro

  • Google Pixel 7

  • Google Pixel 7 Pro

  • Oppo Reno 10x Zoom

    Unfortunately, you can't use such devices for taking accurate HRV measurements.

In such cases, we recommend taking HRV measurements with compatible HR monitors or Samsung Galaxy Watch.

How many measurements per day can I take?

In the PRO version, users can take an unlimited number of 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.

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