Smart or intelligent sensors are integrated physical units embedded with sensors, processors, and communication devices. The sensors also known as edge nodes form the lower-most tier in the internet of things architecture. These devices rely on cryptographic technique to ensure 'root of trust' for the users. The implementation attacks namely side-channel attacks (SCAs) pose a dangerous threat for the cryptographic implementation in the edge nodes since the attacks are undetectable by nature. Among the different categories of SCAs proposed in the literature, power analysis attacks (PAAs) are vastly studied and widely employed because it can be mounted with relatively inexpensive equipment. In this study, the different categories of PAAs along with the countermeasures are reviewed in detail. The impact of the SCA on the edge nodes is examined along with a case study on medical sensor nodes.