This working prototype of mobile security robot is capable of patrolling an area without human interaction and provide feedback of the state of its surrounding when it detects the intruders motion. It can replace humans or animals as guards to overcome security problem. It is a low cost mobile robot which is easy to use. This mobile security robot operates mainly indoors and navigates itself on a flat horizontal surface designed to avoid obstacles in its way such as furniture, wall and human in close proximity. This robot is programmed to move autonomously in a designed area to patrol and detect current motion. When it detects movement, the robot will respond by giving a sound signal to indicate the intruder.