an automatic signal ( usually a sound) warning of danger

warn or arouse to a sense of danger or call to a state of preparedness; " The empty house alarmed him"; " We alerted the new neighbors to the high rate of burglaries"

a warning serves to make you more alert to danger

condition of heightened watchfulness or preparation for action; " bombers were put on alert during the crisis"

not unconscious; especially having become conscious; " the patient is now awake and alert"

very attentive or observant; " an alert and responsive baby is a joy"; " caught by a couple of alert cops"; " alert enough to spot the opportunity when it came"; " constantly alert and vigilant, like a sentinel on duty"

mentally responsive; " an alert mind"

Watchful; vigilant; active in vigilance.

Brisk; nimble; moving with celerity.

An alarm from a real or threatened attack; a sudden attack; also, a bugle sound to give warning.

On the watch; active; brisk; ready; vigilant.

The lookout; a guarding against surprise; as, to be on the alert.

Alertly.

Alertness.

Watchful: brisk.

On the watch; ready.

Watchful; brisk. Upon the alert, upon the watch.

Watchful; on one's guard; sprightly; nimble.

He won't risk another attempt, now that he is aware we are on the alert. – The Green Mummy by Fergus Hume

Her eyes were brown, alert, and fun- loving, her manner quick, and her speech enthusiastic. – Abroad with the Jimmies by Lilian Bell

We in responsible positions, and myself most of all, were on a constant alert, ready for instant decision or personal attention to a mass of new detail at any moment. – Greener Than You Think by Ward Moore

He was alert enough, but it's a big house to watch. – The Film Mystery by Arthur B. Reeve

The police, according to Frank, were much on the alert, but were very secret. – The Eustace Diamonds by Anthony Trollope

Naturally she was much on the alert to- day, for it was more than possible that Diva's dress was finished and in evidence. – Miss Mapp by Edward Frederic Benson

To- day, however, there was something on her mind, and she was not as alert and successful as usual. – Cumner & South Sea Folk, Complete by Gilbert Parker

The thought kept them alert. – Three Sioux Scouts by Elmer Russell Gregor

The whole population was on the alert, and the baffled Frenchmen were forced to retire from the gates, to avoid being torn to pieces by the citizens whom they had intended to surprise. – Project Gutenberg History of The Netherlands, 1555-1623, Complete by John Lothrop Motley

No wonder he learned English quickly, for he was ever on the alert- no strange word escaped him, no unusual term. – Composition-Rhetoric by Stratton D. Brooks

Beneath the trees it was blacker, but the keeper well knew his way, and at the end of a few minutes he had spread out his forces some fifteen yards apart, with a whispered word to be on the alert. – The Star-Gazers by George Manville Fenn

At first thought it seems strange that a bird should be most at home when he is away from home; but in the one case he has nothing but his own safety to consult, while in the other he is thinking of those whose lives are more to him than his own, and whose hiding- place he is every moment on the alert to conceal. – Birds in the Bush by Bradford Torrey

A person who knew him says he looked like a bird himself; keen, alert, wide- eyed. – Locusts and Wild Honey by John Burroughs

All alert, Curlie sat listening for any further message which might reach him. – Curlie Carson Listens In by Roy J. Snell

But Blackburn and his men were alert. – The Trail Horde by Charles Alden Seltzer

And he who has learned to observe, and who is alert to the appeal of nature, has no small part of his education already assured. – The Mind and Its Education by George Herbert Betts

Yet he was a cool- headed fellow, always alert for that which might bring him gain. – The Power and the Glory by Grace MacGowan Cooke

Those whom it was most important to keep in ignorance were the first on the alert. – The Secret Memoirs of Louis XV./XVI, Complete by Madame du Hausset, an "Unknown English Girl" and the Princess Lamballe

Instantly he was on the alert. – The Haunted Bookshop by Christopher Morley