Tool failure is one of the primary causes of failure in computer numerical control (CNC) machine tool machining. Such necessitates condition monitoring of CNC machine tools to improve the effectiveness of failure-free operation and decrease the probability of waste and equipment failure caused by tool failure. This paper proposes a novel method based on the Internet of Things (IoT) and Petri nets (PNs). In the first iteration of the proposed method, a PN model is designed to represent the milling machine and guarantee the model's liveness. Then, the developed model is integrated with the IoT model to monitor the tool condition based on the obtained data from the sensors. The experiment results demonstrate that the developed method can represent the tool's wear state and provide a timely reminder to replace the tool.