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New sensor called FaceBit can tell if health mask fits properly and provide other data. Designed for workers, device also could benefit public eventually.

A new smart sensor that measures face mask fit may come in handy for workers who need to know their masks are working, Northwestern University researchers say.

FaceBit, as it is called, also measures heart rate and respiration, similar to the fitness wearable Fitbit, but with special attention to mask fit.

The quarter-sized device fits onto any mask with an accompanying magnet. It sends information to a smartphone app that displays the results and alerts the wearer to concerning conditions such as an elevated pulse or a leak in the mask.

The device checks mask fit by measuring the change in resistance to the wearer’s breathing, co-developer Josiah Hester said. Hester is an assistant professor of computer science, computer and electrical engineering at Northwestern’s McCormick School of Engineering.

Health care workers now must undergo cumbersome 20-minute tests to ensure proper mask fit. The test involves wearing a shield over the face, then spraying a sweet or bitter aerosol at the face and seeing if the worker can smell it. If so, the mask isn’t tight enough.

The FaceBit likely won’t replace such tests, but could give warnings if a mask gets dislodged or otherwise starts leaking, Hester said.

The device also measures respiration by the force of each breath, and heart rate by tiny motions of the head caused by the rush of blood through the neck.

As originally conceived, users might include health care workers but also others who need a good mask fit, such as miners and those who do environmental cleanup or work with toxic chemicals.

But now that the U.S. Centers for Disease Control and Prevention has recommended that the public may choose to wear tightfitting N95 and KN95 respirators to get better protection against COVID-19, there may be more of a public interest in mask fit.

“It’s definitely moving where fit will matter more because omicron’s so transmissible,” Hester said. “We know mask fit is a big industry problem, but now it’s much more important to the general population.”

Northwestern engineers developed about a dozen prototype FaceBits over the past year with a $200,000 grant from the National Science Foundation.

Researchers shared their information in an open source format online, so that other researchers can replicate and expand on their work.

Before the device could be mass-produced, it would need clinical studies to prove its use in the field, which could take some time. At an estimated production cost of $40 to $110 per device, it’s not insignificant, but cheaper than a Fitbit.

A tiny battery powers the device, but FaceBit can extend the battery life by harvesting energy from the user’s breathing and motion or from the sun. The battery lasts about 11 days between charges.

The research was published recently in the Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies. The study found that FaceBit’s accuracy was similar to clinical-grade devices.