In my thesis I demonstrate some passive positioning technologies, and introduce our implemented system based on radio tomographic imaging (RTI). In the first two chapter I specify these technologies using the literature and present a few algorithms for wireless systems. Our system was created in a project with the leadership of Győző Gódor at the Department of Networked Systems and Services which started in January 2013. I joined in this project during the second semester of 2012/2013. The system has three main components: data collecting and communication between the nodes, data processing by the server and implementing a positioning algorithm for it, and developing an application that can display the results. One of my tasks was to implement the data processing in MATLAB. At the beginning we didn’t have any node so we used simulated data for testing the algorithm. I also created a user interface where the user can configure the program, set the main parameters and change between simulation and measurement mode. During operation the result of the algorithm is also displayed in an interactive window where the user can read information about the state of the system and set the parameters of the sensors. Furthermore, the processed image can be displayed on a mobile device too with an Android application which was developed by Dávid Tóth. The system can locate people on an observed area which can be very useful for example in emergency situations where firefighters have to find people in a room filled with smoke or tracking big wares in a warehouse.