I would like to have a robot w

I would like to have a robot who acts like an alarm, it would control rooms, front and backdoor by walking around the house. If it noticed movement it would message the owner and start filming the envirement (to get the source of movement on camera). The cost saved for placing an alarm system could be invested in a robot, who can be put to use for other stuff when the owner is home. In addition it could act as a smoke detector to look for fire.