No other external hardware is required, all you need is your smartphone.
Camera is not used !!!
Measuring is based on motion sensors.

Your recovery heart rate, the speed at which your heart rate returns to normal after exercise, can indicate physical cardiac condition and the risk of certain diseases. People whose heart rate recovery time is long are at a higher risk of death than people with shorter recovery times regardless of physical condition or other risk factors. Measuring heart rate recovery rates is one way to tell whether an exercise program is effective.

People in better cardiovascular condition tend to have lower heart rates during peak exercise, and return to their resting heart rate more quickly after physical activity. Before embarking on a new exercise regimen, record your resting heart rate as a baseline and see how it improves over time with your new fitness efforts.

How to measure your recovery heart rate?

Choose an activity that’s going to get your heart pumping. Go for a brisk walk or run around the block, jump rope, use an elliptical trainer, or do any activity that will increase your heart rate. Once your heartbeat is approximately within target zone with 50 - 90 percent of intensity see section about heart rate, stop exercising.

Instructions:
* Put your phone in the armband
* Press start button
* Wait for end of measurement, it takes 2 minutes
* That's all!

App Features:
* Measures your Recovery Heart Rate with your smartphone
* Graphs illustrate your measurements
* Determines of target heart rate zones
* Personal profile
* Share results on Facebook (open graph story)
* Share results on Twitter
* Share results on Google+

Pro Features:
* Unlimited number of measurements
* Unlimited storage of results
* No ads