“Instant Heart Rate” Android & iPhone application measures your pulse

November 3rd, 2010

The “Instant Heart Rate” application for Android and iPhone measures your pulse using your phone’s camera.

How does it work?

The “Instant Heart Rate” application works similarly to a medical pulse oximeter. It makes use of the fact that in many smartphones today there is a bright light source (flash) right next to the camera lens. The application turns the flash light on and asks you to place your finger lightly over the camera. Using light reflected from the flashlight by your finger, the application measuring small changes in the colour of your blood. These small changes in colour correspond to individual heart beats.

With relation to an oximeter, the light source acts as a replacement for the LEDs whilst the camera replaces the photodiode. The other difference is that whilst most oximeters measure the colour of the light which is transmitted through the finger, this application measures the colour of the light which is reflected from the finger.

What changes in blood colour does the application measure?

When your heart beats, oxygen is pumped around your body. The blood becomes more oxygen rich and it’s colour changes very slightly. The guys at Oximetry.org summarise this whole process well (hemoglobin is a protein in blood which transports oxygen around the body):

The principle of pulse oximetry is based on the red and infrared light absorption characteristics of oxygenated and deoxygenated hemoglobin. Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through. Deoxygenated (or reduced) hemoglobin absorbs more red light and allows more infrared light to pass through… With each heart beat the heart contracts and there is a surge of arterial blood, which momentarily increases arterial blood volume across the measuring site. This results in more light absorption during the surge.

How well does it work?

I was sceptical about this application to begin with but it seemed to give me fairly decent readings. Whilst at rest, it gave me a pulse rate in the mid-60s which is roughly what I would expect as a ballpark figure. A few minutes later, after doing a round of press-ups, the application gave me a heart rate in the region of 95-100 which again is roughly what I’d expect. I haven’t compared the measurements to an actual heart rate monitor to determine the accuracy but it would seem like the figures are at least in the right ballpark and certainly aren’t plucked out of thin air.

I would expect the accuracy of the application will depend on several factors such as background light sources, the quality of the camera and perhaps the location of the flash on your phone. I certainly wouldn’t trust this application for a medical measurement or even sports training, but as a fun application it seems to do the job.

Drop us a comment below and let us know what your experiences of the app are.

What are the limitations of the application?

under my umbrella
Creative Commons License photo: TheAlieness GiselaGiardino²³

The first key limitation is that we don’t really know how well it works. My friend (a medical student) checked my pulse independently of the application and reckons the application had an error of about 5-10 beats per minute on my HTC Desire. That said, the accuracy of the measurement is likely to depend on many factors such as the model of phone, where you use it, etc. This makes it difficult to know how trustworth the measurements from the application are.

The second limitation is that it doesn’t seem practical as an every-day application. I can’t imagine taking my HTC Desire down to the gym with me and actually using the application as I exercise. Not only would you look like a muppet, I’m pretty sure the flashlight would very quickly drain the battery and it will become difficult to use the application when your palms start to get a little sweaty.

Where can I download “Instant Heart Rate”?

You can download the application for free from Android Market. Scan the following QR code or if you’re reading this article from your Android handset, simply tap on it:

iPhone users can download the application from the iTunes Store but you’ll have to pay $1.99 for it.

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About Ken

Ken Lo

My passion is helping people to get the most out of their mobile phone. I've been blogging at Ken's Tech Tips since 2005.

Aside from writing about mobile technology, my interests are in software development, digital marketing and physics. Outside of the blog, I work with numerous technology companies helping them to explain their product and helping them to market it to consumers. Please get in touch for more information.

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