Determining the required number of sensors to be deployed is a critical decision for surveillance wireless sensor networks. In this paper, we discuss the trade-off between the number of sensors and the breach detection probability considering the effects of sensor parameters. We present the weakest breach path problem formulation and provide a solution by utilizing the Dijkstra's shortest path algorithm. We propose a method to determine the required number of sensors to be deployed and to gain insight about the surveillance performance of the network, the maximum detection probability on the weakest breach path is considered as the performance measure. (C) 2005 Elsevier B.V. All rights reserved.