Wireless microsensor networks have gained great momentum due to collaborative research efforts on various disciplines. It has made many useful applications possible. In a typical sensor network application, in order to operate for a long period of time, sensor nodes need to conserve energy. In this paper, a multi-hop tripwire detection and cueing scheme is proposed for energy conservation in wireless sensor networks. It uses a cueing protocol and a detection algorithm to enable a two-tier sensor network for energy conservation. The proposed scheme overcomes the false alarm problem and the exposed alarm problem in sensor network applications. For a typical application scenario of sensor networks, our simulation results show that a two-tier sensor network employing the proposed scheme can reduce energy consumption by about 55% when compared to a homogeneous sensor network.