A doctor places a stethoscope on the chest and listens: lub-dub, lub-dub. The rhythm is there, but how do you measure it when it's noisy around and the patient can't lie still? Conventional devices look for sharp peaks in the heartbeat recording, like catching hammer blows. But if the hammer hits a pillow instead of an anvil, the peaks blur and the device gets lost.

CORAL, the new method, works differently. It turns the signal recording into a picture resembling ripples on water from a thrown stone. Each circle of this ripple is a repetition of the rhythm. The clearer the circles, the more stable the pulse. The program looks at the pattern and immediately sees how many beats per minute and how evenly the heart beats. It's like examining a fingerprint: you don't need to look for individual lines; the pattern is visible as a whole.

The scientists tested CORAL on recordings from intensive care, from newborns in the neonatal intensive care unit, and from healthy people who simply walked down the street with a sensor on their chest. Heart rate matched the readings of precise medical devices with a correlation coefficient of 0.99 (where 1 is a perfect match). Even when the signal was so weak that conventional detectors gave up, CORAL found the rhythm.

Ripples on water fade, but if you throw pebbles at regular intervals, the circles repeat. The heart is that pebble, and CORAL is the observer who looks not at the splash but at the expanding circles. This way, you can hear the pulse even through noise.