Definition of "heads up" []

• Used as a warning to watch out for a potential source of danger, as at a construction site. (interjection)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The extra-poor men and the extra-good men always stick their heads up above the dead-level of good-enough men; the first to holler for help, and the second to get an extra reach."
• "She turns on Stevens and heads up the South Hill, once the concentrated prime real estate in Spokane."
• "Jens Foerster, a German psychologist, has assumed the role of experimental Qi Gong master by conducting some fascinating research on how people infer their attitudes from their nonverbal behavior.4 Here is a typical Foerster experiment: People are asked to move their heads up and down for some spurious reason or to move their heads left and right while they watch some stimuli."