Various forms and models of safety devices that are very rapid are encouraged because of developments in the security system in each year. In smart buildings, the ability to detect the presence of building residents is one of the important factors to control the use of resources and create a safe atmosphere for the occupants. Therefore, it takes a system that can find out the number of people in the room. In systems research requires tools and materials that support the manufacturing process. The research method is done by collecting some data that serves as a literature review of the system that will be designed. Literature reviews are taken from several journals and others. Literature review collected contains descriptions of prototypes, research steps, hardware design and software design. The system is designed using Arduino and is connected to an Android smartphone. From the test results in this system, it is found that there is an ability in the system to detect objects in the form of humans coming out and entering the room and can calculate the number of people in the room. This system is also able to display data on the number of people in the room on 16x2 LCD and Android smartphones through the Spy On Cheating application.