According to the OED, 'heads up!' as a phrase meaning 'watch out!' is (surprise, surprise!) American in origin - first recorded in 1916. As an adjective (a 'heads up alert') it is first found in 1979. As a noun ('a heads up on a sale') it is recorded in 1981. Roz's hate phrase 'giving a heads up' first appears in 1988, in the Los Angeles Times.
How about 'giving a warning' or 'giving an alert' if you want to avoid the phrase?