monitor

any of various large tropical carnivorous lizards of Africa and Asia and Australia

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

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

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

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

someone who supervises (an examination)

keep tabs on

check, track, or observe by means of a receiver