The digital era has witnessed giant strides in the utilization of security systems, which perform certain pre-programmed tasks when a secured zone is breached. The prevailing traditional security systems have evolved embracing the cutting-edge technologies from time to time. The avalanche-like explosion of things and their connectivity through Internet have opened several new boulevards of exploration. The unification of security system based on the IoT platform has the potential of interrelating real time with the devices and makes them smart, with issues like privacy. To keep the issues in the bay, a new intrusion detection system is the need of the hour. Hence, a wireless intrusion detection smart security system is designed and developed to overcome the research gaps in the existing systems. The smart security system is built on the Internet of things. The system is a lightweight, low cost, extensible, flexible wireless IoT-based-smart security system which will permit the mobile devices and computers to remotely trail the happenings at the location, record the activities and save them in the prefixed cloud storage account. The system uses the hardware (things) to sense and fetch the data which is processed by the embedded software. On the occurrence of an abnormal activity (like breaching by an intruder), a valid signal is detected, and it sends signal to the board directing it to run the alert module. The alert module activates the GSM API to immediately alert the end-user by mobile. This system thus provides a wireless, incessant service to all the stakeholders by phone regarding the breaches occurring in the environment. This implemented smart security system using IoT with mobile assistance also integrates the various alarms, sends alert as pre-programmed, tracks the movements automatically, uses the state-of-the-art appropriate latest technologies to alert the concerned stakeholders and waits for actions to be taken. © Springer Nature Singapore Pte Ltd 2020.