A radiation detection system has been developed utilizing one board-type radiation sensor, a microprocessor and android tablet software. Information regarding the environmental radiation dose is saved in a CSV log file in the tablet associated with GPS position data. Furthermore, viewer software has been designed for the radiation heat map and time-series graph. The GPS tracking function has been very important for visualizing the radiation data in the heat map since the nuclear power plant accident in Fukushima Japan. This visualization helps users to understand the environmental radiation level, and the log data is used to check hot spots in the contaminated area. In order to develop a long-term measuring system, a low-power custom CMOS detection circuit has been designed using a 0.6-μm three-metal process. The power consumption of the developed circuit is 2mW.