Your headphones could be used to measure your pulse

Researchers have developed software that could let you measure your pulse using nothing more than your earphones and a smartphone. The tech measures the air pressure in your ear canal, taking advantage of the seal made by earphones. As your arteries pump blood, it causes tiny movements in your eardrum at a frequency of about 1Hz. Using the earphones' speaker as a microphone, the software can detect and interpret this movement to determine your pulse rate.

via Tech News Headlines - Yahoo! News http://www.theverge.com/2013/10/27/5031006/your-headphones-could-be-used-to-measure-your-pulse