Apple watch 1: https://pubmed.ncbi.nlm.nih.gov/28709155/ 268 citations on Google Scolar to this date. https://scholar.google.com/scholar?hl=de&as_sdt=0%2C5&q=Variable+Accuracy+of+Wearable+Heart+Rate+Monitors+during+Aerobic+Exercise+&btnG= Apple watch 3: https://pubmed.ncbi.nlm.nih.gov/31555543/ 82 citations to this date: https://scholar.google.com/scholar?hl=de&as_sdt=0%2C5&q=Accuracy+of+commercially+available+heart+rate+monitors+in+athletes%3A+a+prospective+study+&btnG= BITalino Validation of a Low-Cost Electrocardiography (ECG) System for Psychophysiological Research (Sensors (Basel)): https://pubmed.ncbi.nlm.nih.gov/34209063/ “Overall, the results of the present study demonstrate good agreement between an inexpensive DiY system and an established …