A Wireless Sensor Network (WSN) consists of spatially distributed sensors (often called as nodes) which are constrained in their size, cost and batterylife. WSN is used for monitoring, surveillance and tracking purposes. A major challenge in WSN is that the WSN are vulnerable to numerous physical attacks and most of the traditional network security techniques can’t be implemented due to the wireless and shared nature of communication channel, untrusted transmission, deployment in open and unattended environments, and limited resources. In this paper we consider a typical threat known as Node Replication Attack alias Clone Attack. In this attack, an antagonist physically captures a sensor node and extracts its credentials like ID, cryptographic key etc. Using this information the antagonist prepares hundreds or thousands of replicas and deploys them in the WSN probably to paralyze the network or its applications. Since the replicas or clones have the same valid ID and valid key as that of the original node, they pass through during authentication tests. In this survey, we explore the various available detection techniques and demonstrate their merits and limitations. © Research India Publications.