A broken CD or DVD or other type of optical disc is a serious problem and one that will likely lead to loss of information stored on this media. A broken optical disc refers to a disc that has split into two or more pieces or perhaps a disc simply missing one piece.
A motion detector is a device that detects moving objects, particularly people. A motion detector is often integrated as a component of a system that automatically performs a task or alerts a user of motion in an area.
They detect heat as it moves through their field of view. When the heat level changes in an area the detector assumes this is motion. If you put it behind glass, especially energy efficient glass, this will greatly reduce the amount of infrared that gets through to the sensor and in most cases will not trip the sensor.