someone who supervises (an examination)

someone who gives a warning so that a mistake can be avoided

display produced by a device that takes signals and displays them on a television screen or a computer monitor

electronic equipment that is used to check the quality or content of electronic transmissions

a piece of electronic equipment that keeps track of the operation of a system continuously and warns of trouble

any of various large tropical carnivorous lizards of Africa and Asia and Australia; fabled to warn of crocodiles