A piezoelectric power generator or harvester can convert impact energy from various mechanical vibrations of daily life into electrical energy. It is an environmentally friendly power generating system. Recently, battery powered RFID tags have attracted attention as a new technology for commodity identification and management in the ubiquitous computer society. However, the need for periodic battery exchange is a major disadvantage of such active RFID-tags. This study describes possible applications of piezoelectric generators to active RFID-tags. As examples of RFID-tag applications enabled by a piezoelectric generator, we propose a safety system to monitor children going to and returning from school as well as a network system to monitor the utilization of a conference room. Experimental results are presented.