You might not be thrilled that face masks are a part of daily life during the COVID-19 pandemic, but they could soon be useful for more than protecting others and yourself. Researchers at Northwestern University (including battery-free Game Boy creator Josiah Hester) have developed a "FaceBit" Face Mask Sensor that can track a wide range of health data from inside an N95 mask. The magnetically-attached unit can gauge your heart rate using the subtle head movements from blood pumping, and can detect leaks or a poor fit by looking for sudden dips in mask resistance.

Those measurements, in turn, can help the Sensor detect a slew of other conditions. Heart and breathing data could let you know when you're stressed and need a break. And while the sensor won't replace an N95 fit test (to verify a proper seal), it's capable enough to help you maintain that fit over the course of a long day.

You might not have to charge the sensor, either. While there is a battery in the prototype, the sensor uses breathing force, heat, motion and the Sun to extend the mask's longevity to 11 days. Hester eventually wants the mask to be battery-free.

FaceBit will need to go through clinical trials and other tests before it's ready for real-world use. However, Hester's team has already released the project code and hardware to the public to help others build and verify it. While you probably won't buy one of these for personal use, it could be crucial for hospitals eager to keep workers safe and prevent burnout over long shifts.