Lasers have many uses, including detecting the presence or absence of objects by detecting when a laser beam is received by a sensor. A laser transmitter may send the laser beam across a void to a sensor. When the laser beam is received by the sensor, there is no opaque object in between. When the laser beam is not received by the sensor, an object may be present. Another reason why the laser beam may not be received may be that the laser or its sensor have been misaligned or maladjusted.
A fixed laser beam may sense the presence or absence of an object using a straight beam of light. Such a sensor only detects the presence or absence along a line from the laser source to the sensor. A scanning or moving laser may be deployed to scan a planar or three dimensional area, provided that a sensor is able to detect the laser beam in the areas being scanned.
The alignment and calibration of a laser transmitter and receiver can be a tedious operation in some cases. In some hostile environments, the lasers or their sensors may be bumped, moved, or otherwise may be misaligned, which may inadvertently cause the laser to not be received. When such a condition is found, a technician may be dispatched to realign and test the system, then place it back in service.