In this study, we develop a vision-based safety driver assistance system (DAS) for use with motorcycles. DASs have been studied by researchers and developed by car companies as a tool to avoid traffic accidents. However, existing studies have seldom focused on motorcycle riders. In Taiwan, the prevention of motorcycle accidents cannot be ignored when developing safety DASs since they are involved in a significant percentage of traffic accidents. This paper proposes a safety DAS for motorcycles which can obtain an input sequence from a smartphone, detect the distance between the owner's motorcycle and an obstacle ahead, and output warning messages if necessary.