Human resources are continuously gaining importance in association with construction site management. With increasing interest being shown in the use of state-of-the-art technologies such as radio frequency identification (RFID) in site management, we developed a device based on infrared radiation and ultrasonic sensors for application in the management of human resources, especially labour safety management. We tested sensors and optimized the sensing range and angle of the device, which could detect workers using an infrared sensor that senses body heat and an ultrasonic sensor to measure the object's distance. The device allows a manager to determine where workers are, and how far they are from the point of sensing. This paper shows that the device can prevent fatal accidents such as falls. In doing so, it addresses a key issue in the management of safety on work sites.