With the world becoming more and more advanced in technology, every section of our society is dependent on computers and internet. Many interactions, data storage and data retrieval takes place over the internet. And with so many interactions comes the need to secure this data. Many researchers have built the Intrusion Detection Systems for the same. Many networks exist. One such network is of IoT. Furthermore, Internet of Things (IoT) is a fast growing network in which objects interact with other objects via the Internet. And IDSs are also required to protect such objects from unauthorised access and other vulnerabilities. So many physical objects including cars, refrigerators, watches, household objects, etc. interact with one another. There is high scope of expansion of such network in future and new attacks will come forward. For such new attacks, new Intrusion detection approaches will be explored. Here we explore some existing IDSs for IoT. We have also done comparative analysis of different IDSs for IoT based on different features like placement strategy, type, attacks handled, etc. Then we implemented 2 well know attacks, DIS attack and Version attack, on Cooja to study their impact on the network by analysing power consumption values of the nodes. Through statistical analysis and outlier detection we found out how a malicious node affects other nodes in the network.