Infrared motion detector circuit

Here is the circuit diagram of an infrared motion detector that can be used to sense intrusions.Infra red rays reflected from a static object will be in one phase, and the rays reflected from a moving object will be in another phase.The circuit uses this principle to sense the motion.The IC1 (NE 555) is wired as an astable multivibrator .The IR diode connected at the output of this IC