The journey to wireless network from wired network has been a worldwide development in the past few decades. The mobility and scalability bring by wireless network made it achievable in many applications. Among all the contemporary wireless networks, Wireless sensor network is one of the most important and unique applications. On the contrary to traditional network architecture, WSN does not require a fixed network infrastructure; every single node works as both a transmitter and a receiver. Nodes communicate directly with each other when they are both within the same communication range. Otherwise, they rely on their neighbour’s to relay messages. The self-configuring ability of nodes in WSN made it popular among critical mission applications like military use or emergency recovery. However, the open medium and wide distribution of nodes make WSN vulnerable to malicious attackers. In this case, it is crucial to develop efficient intrusion-detection mechanisms to protect WSN from attacks. With the improvements of the technology and cut in hardware costs, I am witnessing a current trend of expanding WSNs into industrial applications. To adjust to such trend, I strongly believe that it is vital to address its potential security issues. In this paper, we propose and implement a new intrusion-detection system named Enhanced Adaptive Acknowledgment.