Monitor your heart beats per minute without a camera. Just put your fingers on your neck or wrist to get your pulse, and then start tapping the screen with the same frequency. Your heart frequency will be displayed in less than a second! No need to position your finger, hold your breath, or any sort of those things.
Apart from measuring your heart, you can also find the tempo for any song. Just listen to the song and keep tapping on the screen. You will find out what is the rhythm of that song. It's addicting!