In this paper, we propose a wireless wearable vibration sensor which is suitable for a touch-based life log system. The vibration sensor is put on a user's fingernail which detects touch-related sound. The system can recognize what kind of objects the user touched or manipulated. The log of the touched objects are stored as user's daily events. One of the advantages of the touch-based log is about privacy. In general, when users share their life log data with others, they do not want to be noticed "WHO" is involved. The touch based logs usually have no such particular data. Our proposed method can be used for socially shared life log system. We prototyped a wearable sensor system and used it in a commuter train.