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.
There were quite a few issues to overcome to achieve this feat. Even the most expensive earphones don't make for a completely-enclosed space, and ambient noise can obviously interfere with measurements. The research team says that its software is now able to isolate the pulse even without a perfect seal thanks to undisclosed "signal processing technologies." The system was demonstrated using a pair of off-the-shelf earphones, and the team believes that if its signal-processing techniques are added to a smartphone, it'll be possible to keep tabs on your pulse with no additional equipment.