How a phone camera can read your pulse
Every heartbeat changes the color of your skin very slightly, and a camera with the right software can turn that change into an estimate of your pulse.
A pulse you can’t see
Each time your heart beats, it pushes a wave of blood through your body, all the way to the tiny vessels just under your skin. For a moment those vessels hold a little more blood, and then a little less. Blood absorbs light, so as the amount of blood changes, your skin reflects slightly different amounts of light.
The change is far too small for your eyes to notice. A camera is different. It records many frames every second, and each frame stores precise color values. Compare those values over time, and the rhythm of your heart starts to appear.
Remote photoplethysmography, in plain words
The long name for this is remote photoplethysmography, often shortened to rPPG. “Photo” means light, and “plethysmography” means measuring changes in volume. Together, they describe using light to follow how the amount of blood in your skin rises and falls. “Remote” means nothing touches you: the camera works from a short distance away.
You may already own something that uses a related idea. Many smartwatches and fitness bands shine a small green light into the skin of your wrist and read how much of it comes back. A phone camera does something similar with the light already in the room, and with your face instead of your wrist.
From video to a number
The details vary from one system to another, but in general the process has a few steps:
- The software finds your face and follows it from frame to frame.
- It looks at areas of skin, such as the forehead and cheeks, and tracks their color over time.
- It filters out changes that don’t come from your heart, like small movements or shifts in the light.
- What remains is a faint wave that rises and falls with each beat. Counting those waves gives an estimate of your pulse.
The same signal carries more than the pulse. Breathing leaves its own slow pattern in it, which is one way camera-based tools estimate breathing rate. And the small differences in time between one beat and the next relate to heart rate variability, which has its own article.
Why stillness and light matter
Because the signal is so faint, anything that adds noise makes it harder to read. Talking, moving your head, shadows that cross your face and light that keeps changing can all blur the pattern. That is why camera scans ask you to sit still in good, even light for a short while. With Doc24hrs, you hold still for about 30 seconds once your face is framed. Our five tips for a good scan go through the details.
What happens with Doc24hrs
The scan uses your phone’s front camera. The camera video is processed on your phone, and it isn’t uploaded or stored. Signals derived from the video, together with the answers in your profile, go to our scan technology provider to compute your results. They are sent with a generic identifier, not your name or email. Your data is stored and processed outside the U.S., including in Mexico. The Privacy Policy has the details.
What a camera reading is, and what it isn’t
A camera reading is an estimate made from a faint signal. Results such as heart rate and breathing rate are wellness estimates. They can be wrong, and they are not a diagnosis. They are most useful when you compare your own results over time, scanned under similar conditions. If you feel unwell or have questions about your heart, talk to a healthcare professional.
This guide is general wellness information. It is not medical advice, and Doc24hrs results are wellness estimates, not a diagnosis. Talk to a healthcare professional about your health. In an emergency, call 911.
