An "electric eye" alarm detects a break in the beam of light not with a simple "electric" cell but with this type of cell
Dark operate photo eyes become operational when the 
receiver "does not ... Certain types of smoke detector use a photoelectric sensor 
to warn of... [DOC] [TLE] Free Flashcards about PHYSICS - StudyStack [PAR] AN "ELECTRIC EYE" ALARM DETECTS A BREAK IN THE BEAM OF LIGHT NOT 
WITH A SIMPLE "ELECTRIC" CELL BUT WITH THIS TYPE OF CELL... [DOC] [TLE] sensors-transducers.doc [PAR] Thermal sensors vary from simple ON/OFF thermostatic devices that control a ... 
heat energy within an object and detect any physical change to that temperature.