The biggest downside to the glut of wearable electronic devices on the market today is that they all need to be charged. Runtime varies greatly from device to device but in hours or days all have to be plugged in. At some point in the future wireless power might come along and make it so electronic devices can get the power they need from our bodies.
At CES this year a prototype sensor patch was shown off that is able to record data about the hydration level of the wearer and send that data to a smartphone. The sensor patch is very small and is designed to get all the power it needs to operate from the body heat of the wearer. Getting power needed to operate from body heat is one potential way that wearables of the future might cut the need for cords for charging.
What the sensor patch needs is a thermal gradient, which it gets by our bodies being warmer than the surrounding air. The prototype sensor pictured here was developed by North Carolina State University's Center for Advanced Self-Powered Systems of Integrated Sensors known as ASSIST. The little sensor is a sticker that is flexible, measures seven square centimeters, and is able to produce between 40 and 50 microwatts of electricity per square centimeter.
The amount of power it produces depends on the temperature difference between your skin and the air around you. To make the 40-50 microwatts of power the sensor needs a difference of 3-degrees C between the skin and the air around you. When air flows over the top of the sensor, such as during jogging, it can make as much as three times more power. The goal is to eventually be able to drive a wearable display with power generated from body heat.