A cell phone jammer is a device that emits signal in the same frequency range that cell phones use, effectively blocking their transmission by creating strong interferences. The power of the Jammer’s effect can vary widely based on a factors such as proximity to towers, indoor and outdoor settings, presence of building and landscape, even temperature and humidity play a role. Jammer blocks cell phone use by sending radio waves along the same frequencies that cellular phones use. This causes enough interference with the communication of cell phones and the towers to render the phones unusage. Thus jammer can work by either disrupting phone to tower frequencies or tower to phone frequencies. There are four different cell sizes in a GSM network – Macro, Micro, Pico and umbrella cells. The coverage area of each cell is different in different environments. Cell radius varies depending on antenna height, gain and propagation conditions from couple of 100Mtrs to several tens of kilometers. The longest the GSM specifications supports in practical use in 35 kilometers.