We are developing radiation detection applications for smartphones and tablets that monitor cosmic rays. The highly sensitive CMOS camera image sensors in billions of smartphones worldwide can detect charged particles. Cosmic rays can be observed by extracting particle trajectories from digital images. This technology has potential applications in a wide range of fields, including education and astrophysical research. Using smartphones as observing devices and building a global network can collect data more efficiently. In this research, we present the results of cosmic ray observation experiments using CMOS sensors and the results of a smartphone app for cosmic ray detection. In order to accurately detect the minimum ionization trajectory, which is expected to be particularly dark, we have developed a new algorithm and placed the sensor vertically to prevent the detection rate from decreasing, which is a unique attempt in this research.