This works presents the development and evaluation of an IoT-based system designed for monitoring customer engagement through ultrasonic sensing and real-time data transmission. The proposed solution employs an ESP8266 microcontroller to measure the presence and duration of individuals in front of a store display using a filtered ultrasonic distance-measurement algorithm. Timestamp synchronization is achieved via NTP, and the collected data, total visitors, arrival time, and observation duration, is transmitted to the cloud using the MQTT protocol. A Node-RED dashboard visualizes the information, enabling intuitive monitoring of customer behavior in physical retail environments. The results demonstrate that the system performs reliably, with consistent detection, stable wireless communication, and low-latency data visualization. The work shows the feasibility of combining low-cost hardware with lightweight IoT protocols to support decision-making in marketing and point-of-sale analytics.