iOximeter is a smartphone heart-rate monitor, powered by the headphone socket

http://www.blogcdn.com/www.engadget.com/media/2013/11/dsc02651_thumbnail.jpg

Connecting health-monitoring hardware to smartphones is a no-brainer. The phone does the heavy processing, offers up power and screen, and thus makes the hardware cheaper and more importantly , smaller. However, you still need to power the thing, which can be tough when you’re trying to gauge vitals …