Heartbeat Monitor/Detector

This is my first time in this forum so am not sure how to post a message. I need help designing a circuit similar to the heartbeat monitor. I need a very sensitive circuit that can detect a heartbeat while strapped around ones neck or wrist, as opposed to a finger.
Is that possible?

I saw a wristwatch at Walmart for $19.97, that monitored pulse rate...

details

sir, i want to get more information about heart beat counter with its block diagrams and details