on the lookout

Idioms  

1. Also, on the watch. Vigilant, alert, as in Be on the lookout for the twins—they're somewhere on this playground, or He was on the watch for her arrival. Both phrases were originally used with upon. Upon the lookout was originally nautical usage, meaning “on duty being watchful” (as for another ship, rocks, or land); it appeared in the mid-1700s, and on replaced upon about a century later. Upon the watch was first recorded in Daniel Defoe's Robinson Crusoe (1719), and on the watch in Jane Austen's Sense and Sensibility (1797).

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Example Sentences

According to recordings of dispatch audio from San Diego police reviewed by The Times, dispatchers told officers in the field at approximately 11:05 a.m. to be on the lookout for a “possible terroristic threat.”

From Los Angeles Times • May 22, 2026

He’s always on the lookout for situations wherein a government or a central bank makes a mistake that can be exploited.

From MarketWatch • Apr. 28, 2026

Just be on the lookout in case your device or browser needs your permission to update and reboot.

From The Wall Street Journal • Apr. 19, 2026

They will also be on the lookout for possible flashes of light caused by meteorites crashing into the surface of the Moon.

From Barron's • Apr. 5, 2026

If you’re on the lookout all the time does that mean that you’re scared all the time?

From "The Road" by Cormac McCarthy

Related Words

• active
• bright
• careful
• intelligent
• observant
• perceptive
• sharp
• vigilant
• wary
• watchful
• wired
• wise