iPhone and iPad. All main features are free. There are a number of in-app purchases available which add things such as a calorie burn estimator and a pulse waveform among others.
It works using the front facing camera by pointing it at your face. It also works by holding your finger lightly over the rear-facing camera - this works better on an iPhone as it can use the flash to illuminate the finger being used to gain a better reading.
Some of the ways this app can be used are:
Measuring heart rate as part of data logging experiments in Science,
Before and after exercise in PE lessons to measure fitness,
Measuring heart rate when doing different activities (watching scary films, etc.) to see how it is affected by doing those activities.
Time needed to learn how to use it and get going:
The app is very simple to use. It will take around 5 minutes to learn how to use it.
What Cardiio Inc. says about Cardiio:
Cardiio helps you measure your heart rate, learn how the numbers relate to your general wellness, perform effective workouts to get in shape, and track your progress.
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Where to find it:
On the Apple App Store - available for iPad or iPhone.