Sensor applications and Internet of Things (IoT) technology using many sensors and smart devices (IoT devices) have been commercially implemented and are significantly changing our daily lives. However, most IoT devices are vulnerable due to low power consumption and have inadequate physical security protection mechanisms. The information security protection of existing sensors is very limited, particularly when large numbers of smart devices are deployed in smart application systems. This limited protection is a major information security concern and has become an important personal privacy issue. The study of the IoT architecture and security taxonomy in the beginning of this paper will help readers understand our proposed concept for improving the security level of existing systems without taking down the whole deployed system, which is the key contribution of this article. Through an actual case study, we have found that by improving the network planning and security management mechanism and applying network segmentation, monitoring, filtering, and IoT trust connection, we can strengthen the security protection of existing IoT systems. We demonstrated that raising the security level of existing smart health systems will increase market value both now and in the future, and ad hoc IoT security solutions can be feasibly deployed in all sensor application fields.