The aim of this work was to investigate arm gestures as an alternative input modality for wrist-worn watches. In particular we implemented a gesture recognition system and questionnaire interface into a watch prototype. We analyzed the wearer's effort and learning performance to use the gesture interface and compared their performance to a classical button-based solution. Moreover we evaluated the system performance to spot wearer gestures and the system responsiveness. Our wearer study showed that the watch achieved a recognition accuracy of more than 90%. Completion times showed a clear decrease from 3 min in the first repetition to 1 min, 49 sec in the last one. Similarly, variance of completion times between wearers decreased during repetitions. Completion time using the button interface was 36 sec. Ratings of physical and concentration effort decreased during the study. Our results confirm that wearer training state is rather reflected in completion time than recognition perf...