The origins of this phrase are a little obscure, but appear to be from the exhortation of sports coaches or more senior people in the army for the players/troops to look up from whatever is distracting them from the game/drill/war. (Their mobile devices, perhaps?)
Be on the alert or on the qui vive, in other words. There may also originally have been an element of buck up! to it.
Fair enough. But at some point people in business and government started talking about giving their underlings a heads-up [note the hyphen for the noun] – to the point now where it has become one of the most tiresome clichés.
I cringe whenever some passive-aggressive person says, Just wanted to give you the heads-up …
The expression also causes spelling issues for people: either they omit the hyphen in forming the noun (a no-no) or they insert apostrophes in strange places.
To avoid orthographical anxiety – and to keep me from cringeing – please stop using this expression.
And on the subject of cringeing, it’s better to spell that with an e so the soft g is clearly preserved; otherwise, you might be tempted to pronounce it to rhyme with singing (compare singeing). Same goes for bingeing on Netflix.