on call

Idioms  

1. Available if summoned, as in Medical residents are required to be on call at least three nights a week. This expression originated as at call in the late 1500s. Also see at someone's beck and call.

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Example Sentences

New rules will mean reservists remain on call for an extra decade, and lower the threshold for them being called into service.

From BBC

They show the arrival of Alan Jones, the lead detective on call that night.

From The Wall Street Journal

"Battlefield" challenges its rival with smaller multiplayer maps than usual and a "battle royale" mode where players eliminate each other one by one, similar to a popular mode found on "Call of Duty".

From Barron's

It wasn’t just the activists on call — block after block was ready.

From Los Angeles Times

The couple was on call for a small but fast-growing rodent who hissed when annoyed and cried when lonely:

From The Wall Street Journal