Which option listed below would have alerted you to the problem in the situation that an air conditioning unit in a server room, causing some equipment overheated while you were away?

Environmental monitors are used in server and network equipment rooms to make sure that the temperature does not change dramatically. In the case of a malfunctioned air conditioner, the administrator is alerted to the drastic modifications in temperature. Multimeters, TDRs, and OTDRs work with copper-based media.