Definition from Wiktionary, the free dictionary
- In an alert manner; with alertness.
- 1823, Walter Scott, Saint Ronan's Well, Chapter 9, 
- Behind one of the old oaks which we have described in the preceding chapter, shrouding himself from observation like a hunter watching for his game, or an Indian for his enemy, but with different, very different purpose, Tyrrel lay on his breast near the Buck-stane, his eye on the horse-road which winded down the valley, and his ear alertly awake to every sound which mingled with the passing breeze, or with the ripple of the brook.
- 1897, H. G. Wells, The Invisible Man, Chapter 23, 
- I walked fast to avoid being overtaken. Every crossing was a danger, every passenger a thing to watch alertly.
- 1925, F. Scott Fitzgerald, The Great Gatsby, Chapter 1, 
- Miss Baker and I exchanged a short glance consciously devoid of meaning. I was about to speak when she sat up alertly and said “Sh!” in a warning voice.
- 2004, Alan Hollinghurst, The Line of Beauty, Bloomsbury, 2005, Chapter ,
- She was wearing tight white shorts and a grey tank top of Jasper’s, in which her small breasts moved alertly.
- 1823, Walter Scott, Saint Ronan's Well, Chapter 9,