  Circadian rhythms govern biological patterns that follow a 24-hour cycle.
Dysfunctions in circadian rhythms can contribute to various health problems,
such as sleep disorders. Current circadian rhythm assessment methods, often
invasive or subjective, limit circadian rhythm monitoring to laboratories.
Hence, this study aims to investigate scalable consumer-centric wearables for
circadian rhythm monitoring outside traditional laboratories. In a two-week
longitudinal study conducted in real-world settings, 36 participants wore an
Actigraph, a smartwatch, and a core body temperature sensor to collect
activity, temperature, and heart rate data. We evaluated circadian rhythms
calculated from commercial wearables by comparing them with circadian rhythm
reference measures, i.e., Actigraph activities and chronotype questionnaire
scores. The circadian rhythm metric acrophases, determined from commercial
wearables using activity, heart rate, and temperature data, significantly
correlated with the acrophase derived from Actigraph activities (r=0.96,
r=0.87, r=0.79; all p<0.001) and chronotype questionnaire (r=-0.66, r=-0.73,
r=-0.61; all p<0.001). The acrophases obtained concurrently from consumer
sensors significantly predicted the chronotype (R2=0.64; p<0.001). Our study
validates commercial sensors for circadian rhythm assessment, highlighting
their potential to support maintaining healthy rhythms and provide scalable and
timely health monitoring in real-life scenarios.
