on duty

Idioms  

1. At one's post, at work, as in The new nurse was on duty that evening, or The watchman was fired because he was drunk on duty. [Mid-1600s] The antonym, off duty, means “not engaged in one's work,” as in Captain Smith was much more amiable when he was off duty. [Mid-1800s]

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Example Sentences

But as the deaths continued, the neonatal consultants had noticed she was the one person who seemed to be on duty.

From BBC

Recent US media reports have said ICE officials were expected to be on duty at Sunday's showpiece at Levi's Stadium in Santa Clara, the home of the San Francisco 49ers.

From Barron's

On Tuesday, Hames, the senior investigating officer, told jurors he was not on duty when the police response to Xielo entering the water began, which he said would have been "chaotic".

From BBC

"Usually, the acoustic sensor is on duty," he says.

From BBC

“You come on duty at midnight. That’s when operators change the settings on their machines. Once a month, they all get the same sheet, which tells them which rotors to use each day and in what order, which ring settings and plugboard settings. So you set up your machine.”

From Literature