Patent ID: 8451135

Claim:
An anti-masking system for a motion detector including a housing having a lens, the anti-masking system comprising: at least one energy source; a spreading lens configured to receive energy from an energy source and to emit the energy outside the housing of the motion detector; a spreading lens sensor located inside the housing to detect energy emitted from the spreading lens which is reflected back into the housing through the lens from an object located outside the housing; at least one reflector located outside the housing adjacent the lens, the at least one reflector being configured to reflect energy received from an energy source back into the housing through the lens; a reflector sensor located within the housing, the reflector sensor detecting reflected energy from the at least one reflector to determine whether an object is located between the at least one reflector and the lens; a retroreflector located on the housing proximate to the lens, the retroreflector being configured to receive and reflect energy from an energy source; a retroreflector sensor located within the housing to detect energy reflected back into the housing by the retroreflector to determine whether an object is located on the retroreflector; and a controller configured to selectively supply energy from the at least one energy source to the spreading lens, the at least one reflector, and the retroreflector, the controller also being configured to monitor signals from the spreading lens sensor, the reflector sensor, and the retroreflector sensor to determine whether the lens of the motion detector has been masked by an object.