A Review on Bidirectional Visitor Counting Systems for Smart Energy Management

Modern buildings use a growing share of global electrical energy because of rapid urbanization, higher occupancy, and steady demand for comfort-based appliances like lighting, air-conditioning, and ventilation. Studies consistently show that 25 to 45% of a building’s energy consumption is wasted due to human negligence or inefficient manual control of appliances. Therefore, occupancy-based automatic control systems are becoming essential for managing energy in smart buildings. Among these systems, bidirectional visitor counting technology is key. It accurately detects when people enter and exit, keeping a real-time count of occupants in a space. This review paper provides a detailed study of bidirectional visitor counting systems, covering their technological foundations, operational methods, sensing principles, hardware, software algorithms, and performance features. It evaluates a range of technologies, including infrared (IR) beam interruption sensors, ultrasonic distance sensors, passive infrared (PIR) motion sensors, thermal imaging, radio frequency identification (RFID), camera-based systems, artificial intelligence (AI)-based computer vision, LiDAR sensors, and IoT-based hybrid systems. The paper also discusses design challenges such as environmental interference, difficulties in detecting multiple people, line-of-sight issues, multi-door synchronization, privacy concerns, and computing demands.