Rob ter Horst tested more than 100 smartwatches:
Peter H. Charton writes scientific papers with those:
The 2023 wearable photoplethysmography roadmap:
https://iopscience.iop.org/article/10.1088/1361-6579/acead2
together with around 50 co-authors:
Peter H Charlton48,1,2, John Allen48,3,4, Raquel Bailón48,5,6, Stephanie Baker48,7, Joachim A Behar8, Fei Chen9, Gari D Clifford48,10,11, David A Clifton12, Harry J Davies48,13, Cheng Ding48,14,15, Xiaorong Ding48,16, Jessilyn Dunn48,17,18,19, Mohamed Elgendi20, Munia Ferdoushi48,21,22, Daniel Franklin23, Eduardo Gil5,6, Md Farhad Hassan21,22, Jussi Hernesniemi24,25, Xiao Hu26,27,28, Nan Ji29, Yasser Khan21,22, Spyridon Kontaxis5,6, Ilkka Korhonen48,24, Panicos A Kyriacou48,2, Pablo Laguna5,6, Jesús Lázaro5,6, Chungkeun Lee30, Jeremy Levy48,8,31, Yumin Li32, Chengyu Liu48,32, Jing Liu48,33, Lei Lu12, Danilo P Mandic13, Vaidotas Marozas48,34,35, Elisa Mejía-Mejía48,2, Ramakrishna Mukkamala48,36, Meir Nitzan37, Tania Pereira38,39, Carmen C Y Poon48,40, Jessica C Ramella-Roman48,41, Harri Saarinen25, Md Mobashir Hasan Shandhi17, Hangsik Shin48,42, Gerard Stansby4,43, Toshiyo Tamura48,44, Antti Vehkaoja48,24,45, Will Ke Wang17, Yuan-Ting Zhang29,46, Ni Zhao47, Dingchang Zheng3 and Tingting Zhu48,12
This gives a total of 52 scientists.