Internet of things (IoT) is a trending technology now a days. Many things are getting shifted to IoT. IoT is related to our daily life actions and hence pose a risk to our privacy if not handled with care. Hence there is need to have secure IoT communication. This paper deals with the various proposed IoT security mechanisms which are capable of authentication, availability, encryption and integrity for secure communication. The paper has been focused on comparative study of emerging security mechanisms of IoT, their strengths and weakness, applications and open research issues. Each and every model has been compared and all the key features of the model have been presented. The IoT has a main requirement which is less power consumption, so the power consumption of various methods used in the proposed models has also been plotted. © 2019 IEEE.