A team of medical researchers and engineers at Google Research has developed a way to use the front-facing camera on a smartphone to monitor a patient’s heart rate. The team has published a paper on the technology on the arXiv preprint server.

Tracking a patient’s heart rate over time can reveal clues about their cardiovascular health. The most important measurement is resting heart rate (RHR)—people with an above-normal rate are at a higher risk of heart disease and/or stroke. Persistently high rates, the researchers note, can signal a serious problem.

Over the past several years, personal health device makers have developed wearable external heart monitors, such as necklaces or smartwatches. But these devices are expensive. The researchers have found a cheaper alternative—a deep-learning system that analyzes video from the front-facing camera of a smartphone. The system is called PHRM.