The clustering algorithm is a kind of basic approach used to reduce energy consumption. It can increase the scalability and lifetime of the network. Energy-efficient clustering protocols should be designed for the characteristics of heterogeneous wireless sensor networks. Here we will discuss about various Distributed Energy-Efficient Clustering (DEEC) protocols for heterogeneous sensor networks. In DEEC, the cluster-heads are selected by a probability dependent on the ratio between residual energy of each node and the average energy of the network. The nodes with high initial and residual energy will have more chances to be the cluster-heads than the nodes with low energy. The DDEEC (Developed Distributed Energy-Efficient Clustering) technique is based on changing the cluster head selection probability dynamically and with more efficiency. The EDEEC (Enhanced Distributed Energy-Efficient Clustering) technique works for three types of nodes in prolonging the lifetime and stability of the network, thus increasing the heterogeneity and energy level of the network. Last but not the least the TDEEC (Threshold Distributed Energy-Efficient Clustering) technique in which the threshold value of a node is modified on which the node decides to be a cluster head or not