Infrared motion detectors are electronic devices, which are used in security alarm systems to detect motion of an infrared emitting source. It detects a change in the thermal energy pattern resulting from a moving intruder and initiate an alarm when the change in the energy satisfies the detector alarm criteria. Infrared radiation exists on the electromagnetic spectrum with wavelengths longer than visible light. Pyroelectric sensors made of crystalline material that creates a surface electric charge when it is subjected to a change in heat. The change in electric charge is measured by a sensor and outputted. This sensor device is sensitive to wide range of wavelengths on the electromagnetic spectrum. A focusing device is used to correctly focus the incoming radiation. This lens can also be used to filter the radiation depending on the material it is made of.