alertness
n.the state of being awake and ready to notice things. It means you are paying close attention to what is happening around you.
n.the state of being awake and mentally alert; the quality of being quick to notice or respond to something. Often used in medical or safety contexts to describe a person's level of consciousness.
“The driver's alertness is very important on the highway.”
“The nurse monitored the patient's alertness to ensure the medication was not causing any drowsiness.”
“Maintaining high levels of alertness during the final hours of the shift requires a combination of physical stamina and mental discipline to avoid critical errors.”
“Most people know it for boosting alertness, but scientists have also been interested in its possible connection to a lower risk of some age-related diseases.”
From alert + -ness.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.