Most of the recent studies on wireless sensor networks deal with the communication coverage. However, for the surveillance wireless sensor networks, sensing coverage is an open research area. In this paper, the sensing coverage area of surveillance wireless sensor networks is studied. The sensing coverage is determined by applying Neyman-Pearson Detection Model and Dijkstra's shortest path algorithm is applied to find the weakest breach path. Although individually not enough, breach probability is an appropriate parameter to justify the required number of sensor nodes and reliability of the network. Analyzing the parameters of the Neyman-Pearson, the most significant parameter is determined to be the false alarm rate. Increasing the false alarm rate, decreases the breach probability because Neyman-Pearson Detection Model tolerates that amount of alarms to be false.