The act of listening, carrying out surveillance on, and/or recording of enemy emissions for intelligence purposes.
The act of detecting the presence of signals, such as electromagnetic radiation, sound, or visual signals, and the measurement thereof with appropriate measuring instruments.
The act of detecting the presence of radiation and the measurement thereof with radiation measuring instruments.
(medicine) The continuous observation of a patient's health condition for any changes which may occur over time, using a monitor or measuring device of some sort.