This paper describes a method for detection of change of state of the indoor environment using the change of the strength of the wireless LAN signals. For the monitoring system of the person's safety in the indoor environment, camera devices are widely used because of the width of view; however, it is difficult to apply the monitoring the person and home environment because of the privacy concerns. We need a method for detection of change of state of the environment using the sensing device that can obtain the global information, but cannot obtain the shape of the indoor environment directly. In this paper, we focus on change of the pattern of the strength of wireless LAN signals because the signal strength has uncertainty and changes due to the change of the state of the environment. The method detects the change of the pattern of the signal strength based on the singular spectrum transformation of the time series of the strength of the wireless LAN signals.Then, the method detects the change of the state of the indoor environment such as the movement of the target persons. Experimental results show the feasibility of the proposed method.