We propose a rapid prototyping method for discovering user-driven application opportunities for personal informatics. The key idea here is that our discovery is realized by empowering users themselves to figure out and express the meaningful information they want to capture and interpret through the prototypes we provide, in an economical and effective way. From the user study, we could extract the key patterns of information usages for family members: (1) recalling life patterns; (2) self-examination; (3) mutual concern; (4) regulation, which are important insights to be considered in developing new applications for personal informatics.