Your heart rate through the night
OPTICAL
Accuracy
96%
Overnight Heart Rate Agreement
scored reading by reading against an ECG chest strap worn the same night
Reference standard
ECG chest strap
Sample size
9 participants
Overnight, the Ultrahuman Ring reads within three beats a minute, on average, of every reference it has been checked against, including a chest strap wired to the electrical signal of your heart. That is scored reading by reading across full nights rather than as one figure a night, which is the stricter test.
96%agreement with the chest strap
2.9 bpmaverage difference
91.5%of readings within 5 bpm
+2.5 bpmthe ring reads high, on average
Your heart rate at night is the quietest, most repeatable signal your body produces, and it is the one the most is built on. It is also read across seven or eight unbroken hours in which you roll onto your hand, press the ring into a mattress, warm up, cool down and pass through every sleep stage there is. A night is a great deal less still for a sensor than it is for you.
Worn on the same nights as an ECG chest strap, your sleeping heart rate sat typically 2.9 beats a minute from it, and 9 out of every 10 readings landed within 5 beats a minute. Two further references give the same answer: 2.4 beats a minute on average from an FDA-cleared sleep device, and 2.6 beats a minute on average from a validated smartwatch. Three different instruments, three answers under three beats a minute.
The second chart plots a sample of the paired readings: the cloud sits tight around the average line across the whole range a sleeping heart rate covers, rather than holding together at one end and falling apart at the other. On a scale where 1 is perfect, the two moved together at 0.94.
The headline is an average difference rather than a correlation. Overnight heart rate is the foundation of virtually every metric the Ultrahuman Ring derives: Recovery, sleep staging, Cardio Age and your VO₂max estimate all sit on top of it, so an error here would reach every one of them.