Drawing on 168 hours of video recordings of smartwatch use, this paper studies how context influences smartwatch use. We explore the effects of the presence of others, activity, location and time of day on 1,009 instances of use. Watch interaction is significantly shorter when in conversation than when alone. Activity also influences watch use with significantly longer use while eating than when socialising or performing domestic tasks. One surprising finding is that length of use is similar at home and work. We note that usage peaks around lunchtime, with an average of 5.3 watch uses per hour throughout a day. We supplement these findings with qualitative analysis of the videos, focusing on how use is modified by the presence of others, and the lack of impact of watch glances on conversation. Watch use is clearly a context-sensitive activity and in discussion we explore how smartwatches could be designed taking this into consideration.