There is great need to limit the use of cell phone at particular places and at particular times. Hence, the use of intelligent mobile phone detector is guaranteed. This work concentrates in designing a system that will dictate the presence of GSM signals from an unauthorized user in restricted areas which will in turn trigger another device to restrict the user from service. The system will be able to jam GSM frequency signal upon detection to prevent the transmitted signal from getting to the users cell phone.Paper is designed to detect the mobile phone in a closed room / place. Whereas this project is aimed to detect the mobile phone where the mobile communication is strictly prohibited like Examination Hall, Hospitals, places of important meeting. As presently we don’t have any technology that should detect the use mobile phones in restricted areas like examination hall instead of checking manually pockets of students before entering in Examination hall and there is chance of having the cell phone with the person if he is not checked properly, however it would be hectic and time consuming for large number of students. so to avoid this problem, an automatic detection of cell phone is introduced. We have a mobile jammers presently used to jam the whole network but in examination hall we have to exclude the faculty members present there and want to detect only cell phone of students. Keeping in view this project mainly focus on designing the mobile detection instrument particularly in examination hall where students misuse mobile phones by making hidden calls, internet connectivity, data transfer,SMS,incomming and outgoing calls etc.I am going to design the mobile detection instrument that automatically detects the activities cell phones in E-Hall and displays this information on GUI on remote computer (administrator) interfaced with mobile detector, like detection messages, Room no, location etc we can extend it as far as we wish, we can add new dimensions to this project, like excluding cell phones of faculty members, determining exact position of detection, calculating distance between position (detected) and detector, increasing range of detection and switching from one room to another on remote computer. Firstly i design the detector to detect presence of activated signal, then I design RF transmitter and receiver to interface this detector with remote computer using arduino Duemilanove (micro controller),then I program microcontroller and design motor control for detector so that it should rotate appropriately, then I design LDR module. I put detector in examination hall, in hall we also make use of LED and buzzer and simultaneously it displays messages to administrator during any malicious activity. The moment the detector detects RF transmission signal from an activated mobile phone, it starts sounding a beep alarm and the LED blinks.