The invention uses five sensors to simultaneously track glucose, lactate, sodium and potassium levels, as well as skin temperature. The data gathered by the sensors are fed to a flexible board of microchips that processes these signals and uses Bluetooth to wirelessly transmit data to a smartphone.

Further Discussion:

Perspiration is a rich chemical full of molecules ranging from simple electrically charged ions to more complex proteins that can be used as an indicator on what is happening inside the human body. Doctors can use sweat to diagnose certain diseases, uncover drug use and reveal insight into athletic performance. Sweat also can be gathered less invasively than blood.

Figure 1  Sweat Sensor Wristband

In the new study at University of California Berkeley, scientists embedded chemical sensors and other devices into a soft, flexible silicone rubber disc that can easily stick to skin. The device is designed to collect and analyze sweat for key biomarkers, or markers of health. For instance, the sensor can show how people are responding to exercise, including whether someone needs to make adjustments, such as drinking more water or replenishing electrolytes. This device could be incorporated into either a wristband or headband.

Figure 2  Biochemical Sensors

The new sensor developed at UC Berkeley can be made into smart wristbands or headbands that provide continuous, real-time analysis of the chemicals in sweat. The prototype developed is composed of five sensors onto a flexible circuit board. The sensors measure the metabolites: glucose and lactate, the electrolytes: sodium and potassium, and skin temperature. A fully integrated system simultaneously and selectively measures multiple sweat analytes, and wirelessly transmits the processed data through Bluetooth to a smartphone.

Sources:
http://news.berkeley.edu/2016/01/27/wearable-sweat-sensors/
http://www.livescience.com/57000-sweat-sensors-use-perspiration-to-track-health.html