This document proposes an improved watchdog technique for intrusion detection in wireless sensor networks. The technique uses a hierarchical model with cluster head nodes acting as watchdogs to monitor network activity within each cell. This is intended to overcome issues with the original watchdog mechanism and reduce power consumption, extending the lifetime of sensor nodes. The algorithm for malicious node detection involves the cluster head eavesdropping on transmissions, comparing messages to a buffer, and raising warnings if messages do not match. Simulation results showed this approach increased network lifetime by around 2611 seconds compared to a non-hierarchical model.