In WSN-based surveillance systems power conservation is an important issue but one must also ensure that the application's objectives are met. In this paper, we jointly address the problem of coverage, disambigation and adaptive scheduling of sensor node's activity to extend the network lifetime while fulfilling a critical surveillance application needs. We first present a distributed algorithm that ensures both coverage of the deployment area and network connectivity by providing multiple cover sets to manage Field of View redundancies. The availability of multiple cover sets leads to a simple but efficient disambigation algorithm. Then, we propose a multiple levels activity model that uses behavior functions modeled by modified Bezier curves to define application classes and allow for adaptive scheduling. Simulation results are presented to validate the performance of the proposed approach.