Remote sensing of position detection and motion detection plays an important part in the welfare filed of human social life. Privacy is a serious problem when detecting human position and motion. A position sensitive device (PSD) only detects the position of a light target without detailed image of human. For detecting multiple light targets, there are various problems such as synchronized light source and noise in daily life space. In this study, we suggest a method using modulated light targets to separate different light targets and eliminate the noise in daily life space for motion detection of a PSD. The target light intensity is modulated with different high frequency source for different targets, so that the noise in daily life space can be eliminated and the positions of different targets can be separated by using band-pass filters. Experimental results showed this method is effective.