Now a days wireless sensor networks (WSN) have wide applications in variety of fields such as military purposes, environmental monitoring, and gathering sensing information in inhospitable locations. But with the increase in use of wireless sensor network the risk of data leakage also increased. The adversary can launch different types of attacks to the network which may subvert the overall functioning of the network. Sometimes the attacker captures some nodes from the network and their credentials will be collected. Some clones of the captured nodes will be created with same credentials and they will be deployed to the network. These nodes act as eavesdroppers of the network data and they will exploit all the privileges of the original captured nodes. So these clones should be detected before they can do much harm to the network. Several algorithms are developed for this purpose.Here a study is carried out on the various novel techniques introduced to detect replicas in wireless sensor networks and their efficiency and performances are analyzed.