on alert

The US Federal Bureau of Investigation became involved early on when the Tesla employee alerted it to Kriuchkov’s plan.

There's also an app—of course there's an app—that will alert you when the mask filters need to be replaced.

The new $100 Inspire 2 activity tracker is different from the Halo, however, with a small screen that provides phone notifications and app alerts.

Mobile phone and broadcast alerts advised people to prepare to evacuate.

District Attorney Michael Ramsey of Butte County, where Paradise is located, confirmed in March that PG&E alerted his office to the allegations and said he was awaiting further information.

Minutes before an airplane hit the water, an alert would go out.

France is on high alert this week after a series of attacks by loners.

I also want to alert you to the broader circumstances of my incarceration.

Spoiler Alert: Do not read if you haven't seen season five episode eight of  The Walking Dead, “Coda”

They walk closely together, tense, and alert in their movements.

It was Carmena, every nerve of her loyal nature on the alert to baffle this pursuer of Alessandro and Ramona.

Then, his hand resting on the handle of the cab-door, this expression suddenly changed to one of alert suspicion.

He is small, alert, brimful of jokes and of years; seventy they say, but he neither looks it nor acts it.

But his eyes and ears were alert, and he was the first to hear the advent of a large body of horses along the main road.

The almost lazy naturalness and simplicity faded gradually out of it, revealing the alert and seductive woman of the world.