1 Feasibility of using stopWatch smartwatch system for passive detection of cigarette smoking in the workplace Paige M Hulls 1,2 , Christopher J Stone 2,3 , Frank de Vocht 1,4 , Marcus R Munafò 2,3,5 , Rebecca Richmond 1,2 , Richard M Martin 1,2,5 , Andrew L Skinner 2,3 1 Population Health Sciences, Bristol Medical School, University of Bristol, UK 2 MRC Integrative Epidemiology Unit at University of Bristol, UK 3 School of Psychological Science, University of Bristol, UK 4 NIHR School for Public Health Research, University of Bristol, UK 5 NIHR Bristol Biomedical Research Centre at the University Hospitals Bristol NHS Foundation Trust and the University of Bristol Corresponding Author: Ms Paige M Hulls (MSc), Population Health Sciences, Bristol Medical School, University of Bristol, Oakfield House, Oakfield Grove, Bristol, BS8 2BN Email: paige.hulls@bristol.ac.uk Christopher J Stone (RSci): School of Psychological Science, University of Bristol, Bristol, BS8 1TU. Frank de Vocht (PhD): Bristol Medical School, University of Bristol, Bristol, BS8 2PS. Marcus R Munafo (PhD): School of Psychological Science, University of Bristol, Bristol, BS8 1TU. Rebecca C Richmond (PhD): Bristol Medical School, University of Bristol, Bristol, BS8 2BN. Richard M Martin (PhD): Bristol Medical School, University of Bristol, Bristol, BS8 2PS. Andrew L Skinner (PhD): School of Psychological Science, University of Bristol, Bristol, BS8 1TU.