Add one more feature to the ever-growing list of smartphone capabilities: measuring blood-oxygen levels.

For people with asthma or COVID-19, absorbing oxygen from the lungs can be an issue. Monitoring oxygen levels is crucial and requires a pulse oximeter, a tiny standalone device clipped to a fingertip. But, one day, tracking blood oxygen might not require specialized equipment.

Researchers at the University of Washington and University of California San Diego have shown that smartphones can be used to monitor blood-oxygen levels as low as 70%. That’s the lowest threshold required by federal regulators who approve oxygen monitoring devices.

The technique involves using a smartphone’s camera and flash along with a specialized deep-learning computer algorithm. Participants in the researchers’ study put their finger over a smartphone’s camera and flash. They were then given a controlled mixture of oxygen and nitrogen to reduce their blood-oxygen levels. In more than 10,000 readings, the smartphone accurately predicted whether people in the study had low blood-oxygen levels 80% of the time.

Researchers say the main benefit of a smartphone-based oximeter is its ubiquity: Almost everyone has a phone, meaning that blood oxygen can be evaluated most anytime at little to no cost.

The phone’s camera records a video, tracking fresh blood flow through the part of a finger that is illuminated by the flash. The camera records how much light from the flash is absorbed by the fresh blood. Those light-intensity readings are then fed into the algorithm to determine the blood-oxygen level.

Someday, your cell phone may help you do more than pay bills or order pizza.