An "electric eye" alarm detects a break in the beam of light not with a simple "electric" cell but with this type of cell
... sufficiently sensitive to detect smoke but at the same time care is 
taken not to... [DOC] [TLE] Patent US4723118 - Magnetic detection system for items on the ... [PAR] To be effective, the array of light beams and electric eyes must be carefully 
aligned, ...