Physical security is a crucial concern in densely populated cities. Traditional security approaches like alarm systems and video surveillance are practical but can be flexible and need more adaptability. This article proposes an Internet of Things (IoT) solution for intrusion detection through mobile notifications. The prototype uses cutting-edge communication and sensing technologies to interact with the physical environment, creating a system that is both effective and adaptable to various security needs. The approach involves developing a prototype that can detect and capture images using a camera when an ultrasonic sensor detects an object within a 3-m range. The captured image is then stored in the host operating system and transmitted to a mobile device using the Telegram messaging service and MQTT protocols through a Node-RED flow. The results demonstrate that this IoT prototype is an adaptable and functional system for safeguarding infrastructure, offering a promising alternative to traditional security solutions.