MEASURE OUR HEART BEAT USING HEADPHONE:

At a medical device exhibition in Yokohama, Japan last week, researchers from the Kaiteki Institute Inc. and Bifrostec Inc. demonstrated a prototype technology that can turn $8 earbuds into a heart rate monitor.
The microphones in a pair of earbuds transmit data about the pressure changes in the ear canal as the eardrum moves, which can be analyzed to determine the wearer's heart rate. According to its creators, the system doesn't require tweaking anything about commercially-available earphones, just using a program to process the signals.

 
 Since the headphones can still be used to listen to music, this could be an easy way to monitor your heart rate at the gym by adding an app to enable your phone or music player to turn the signals from the earphones into a readable heart rate. Motorola has previously offered a line of headphones featuring heart rate monitors, but they will run you a whole lot more than $8.