Numerous developments and applications have been made possible by the quick development of the Internet of Things (IoT) in various fields, including banking, healthcare, smart homes, and smart cities. Smart security systems are gaining popularity due to their adaptability, decreased need for human intervention, increased reliability, time efficiency, and improved threat detection. Although different solutions have been developed as smart systems, limitations include limited coverage, false alarms, flaws in authentication procedures, privacy problems, reaction time, and external dependency. The mentioned issues must be addressed for an efficient smart security system. This paper proposes an IoT-based smart security system to detect threats using machine learning to recognise human faces and objects. This system uses a Convolutional Neural Network (CNN) for face recognition to identify intruders and black-listed objects using the Single Shot Detector (SSD) method. When an unknown person is found, the system notifies the admin through push notification to take additional action. In conclusion, the smart security system yielded promising results, with CNN achieving an accuracy of 94%, precision of 90.91%, recall of 100%, specificity of 85%, F1-score of 95.24%, and SSD achieving accuracy of 90%, precision of 90%, recall of 100%, specificity of 0%, and F1-score of 94.7% for face and object detection, respectively. The potential uses of the smart security system go beyond the purview of this research and can be put into practice in various industries, including finance, healthcare, smart homes, and smart cities. This system may significantly improve security measures and offer a safer environment by utilising cutting-edge technology and machine learning approaches.