In most of the location detection methods in a wireless sensor network, a target node with a device helping location detection exchanges signals with sensor nodes and localizes the target by analyzing the signal changes. However, the active localization method is not suited for the applications such as intrusion detection. Thus, in this paper, we propose a passive localization method for detecting the location of a mobile target that does not have a special device for the location positioning. Sensor nodes with ultrasonic sensors are deployed in the target area to form a virtual grid with the transmission delay of a ultrasonic signal from a sender node to a receiver node. Then, we analyze the delay statistically to detect the location of a moving target. Through experiments in real environments, the implementation possibilities and feasibility of the proposed method were validated.