An automatic alarm system for monitoring personal working status in those sites where watchkeepers are needed is developed. The system is developed by using an automatic control module and a serial port control module based on infrared detection technology according to practical application needs. It incorporates the modern electronic PCB making technology, the Arduino microcontroller technology and the computer programming technology. Compared with other monitoring systems, this system is not only simple and low in cost, but also has several functions of monitoring, reminding, alarm and background logging.