Give a heads up (idiom explained)

heads up is often high ated head as in h a d, heads up, u p. next expression is to give someonea heads upa heads up. And this is when you tell someone about something before it happens. So if reza tells me there's going to be a bus strike in valencia to morrow, and i was thinking of travelling, i might say a thanks for the heads up, reza. Thanks for letting me know.