He wanted to do a little more with the equipment so he ditched the watch and built an Arduino-based heart rate monitor ... it will pulse an output pin with each beat of the heart.

The Geek Pub guide will help get you started with an Arduino pulse sensor. While sensors like this are reliable, it's worth keeping in mind that your heart rate can tell you a lot of different things.

The build combines an EmotiBit sensor platform with an ... From this data, a pulse rate can be derived, and the LEDs flashed with a heart graphic in concert with the rhythm of the wearer’s ...

You may be interested in a project published to the Hackster.io website earlier this year providing instructions on how to create a simple wearable heart rate monitor using an Arduino Nano R3.