The emergence and flourishing of the Internet of Things (IoT) are attracting increasing attention from various business domains and research fields. In fact, for numerous sensors, sensor device management is very crucial to the IoT environment. By reviewing the existing literature, we investigate the sensor device management architecture and visualization technologies. A few of them concern sensor state visualization and management. In this paper, we propose a novel visualization method based on composition map symbols for sensor state visualization. The composition method is based on the integration of multiple graph layers into a new composition symbol, which uses only a few simple graphs to represent various sensors. The method does not require predefining numerous symbols for various sensors and supports the dynamic symbolization in accordance with sensor states. On the basis of the novel visualization method, a system named SensorMon with a lightweight mobile app was developed to validate the effectiveness of our method for maintaining and monitoring sensors. The proposed method and implementation have potential applications in the IoT environment.