Many students are caught copying in their exams and using mobile phone in class or in lecture class. An Arduino based mobile phone detector could reduce the number of students who are copying and prevent the usage of mobile phones in class. Our objectives are to avoid the usage of mobile phones during examinations and lectures and to detect mobile phones in a range of 30-40 meters. Methodology used in this Arduino based mobile phone detector is that an antenna that detects signal between 0.9 to 3GHz. Then the signal level is transmitted to the resistor. The resistor then transmit the signal obtained by the antenna to the microcontroller in the Arduino which is programmed to sound the buzzer when signal from a mobile phone is detected. The circuit operation is 9V DC. When an active mobile phone is placed near the antenna, the detector was able to detect the signal and give output of the buzzer and LED.