The need for an effective and reliable intrusion detection with an alarm system have become vital necessity because of the frequent and rampant cases of burglary. Attack on homes offices, factories, banks etc. is on the increase. With the advancement in technology, motion can be detected by measuring change in speed or vector of an object in the field of view. This can be achieved either by mechanical devices that physically interact with the field or by electronic device that quantifies and measures changes in the given environment. The motion detector is not only used as intruder alarm but also used in many applications like home automation system, energy efficiency system, etc. This project is built using an embedded microcontroller system capable of detecting motion of an intruder in a restricted area and then triggering an alarm system, motion detector system, however passive infrared sensor detected the motion of the person using the person body heat. The passive infrared (PIR) sensor which is the motion detector used in this project is attached to a microcontroller which activates the alarm system and any other attached output device to notify the house owner. The initial testing of the design shows that it worked as expected.