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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 as 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.

You can learn how to achieve high-accuracy measurements here.

Note: On some phones, the flashlight may get too hot for your comfort. If this happens, hold your finger 2–3 mm away from it. Make sure your finger still covers the camera.

How it works

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 of which are conveniently available in a standard smartphone: the flashlight acts as the light source, and the camera serves as the photodetector.

The measured changes are caused by the beating of your heart. 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 precisely detect even the smallest fluctuations. Research supports that this approach is not only accurate but also user-friendly, effectively turning your smartphone into a robust tool for health analysis.

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/iPad devices featuring the Ultra Wide camera/Back Telephoto camera/Back 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

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

  • iPad Pro 11" 2nd gen

  • iPad Pro 11" 3rd gen

  • iPad Pro 12.9" 4th gen

  • iPad Pro 12.9" 5th gen

  • iPad Pro 12.9" 6th gen

The following range of iPhone devices has the Back Telephoto camera:

  • iPhone 15 Pro

  • iPhone 15 Pro Max

The following range of iPhone devices has the Back camera:

  • iPhone 15

  • iPhone 15 Plus

If you own one of the devices listed above, we recommend that you switch to the Ultra Wide camera/Back Telephoto camera/Back camera to improve the quality of your measurements. To change the camera, please open the app Settings → Measurement Device and select Ultra Wide camera/Back Telephoto camera/Back 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/iPad 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:

Finger positions for measurements with iPad Pro 11" 2nd gen, iPad Pro 11" 3rd gen, iPad Pro 12.9" 4th gen, iPad Pro 12.9" 5th gen, iPad Pro 12.9" 6th gen:

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 Back Telephoto camera.

Finger positions for measurements with iPhone 15 Pro, iPhone 15 Pro Max:

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 Back camera.

Finger positions for measurements with iPhone 15, iPhone 15 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 Premium 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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