Consumer‐grade optical heart rate (HR) sensors emerged as promising tools to monitor volume and intensity of physical activity (PA). However, no validation study of optical HR sensors included recent comprehensive validation recommendations, required for facilitating usage for medical purposes. Validity of HR data measured with four consumer‐grade optical sensors, the wrist‐worn Garmin Venu 2S and Polar Vantage M2, and the upper arm‐worn Polar Verity Sense and Scosche Rhythm24 were assessed in 32 participants over 24 h including various laboratory‐based and free‐living activities. Furthermore, validity of time at moderate or vigorous PA intensity zones was analyzed. A medical‐grade ECG served as a reference. Reliability was assessed by analyzing data of laboratory‐based activities during two visits. Across activities, the mean absolute percentage error ranged from 2.2% to 4.7% and intraclass correlation coefficients ranged from 0.91 to 0.98, indicating high validity for all optical sensors. All sensors validly detected time spent at moderate or vigorous intensities (mean error < 10%), except Polar M2 for moderate PA (mean error 12.8%) and Garmin V2 for vigorous PA (mean error −15.9%). Sensor day‐to‐day reliability was high, indicated by a mean absolute error of < 5 beats/min. Upper arm‐worn sensors consistently outperformed wrist‐worn sensors, particularly in activities involving increased arm movement and at higher intensities. Our findings identified an overall high validity of these four consumer‐grade optical HR sensors, also for assessing time spent at higher PA intensities. However, differences were observed between sensors regarding activity subtypes and intensity levels. These data support informed decisions when selecting optical sensors for PA monitoring and intervention.Trial Registration: The study was performed in compliance with the Declaration of Helsinki and its current amendments and was prospectively registered at ClinicalTrials.gov (ID NCT05525000).
