pozor

1. (as a warning) attention!; look out!
   Na ogradi stoji tabla: „Pozor! Visoki napon.“ — There is a sign on the fence: "Warning! High voltage."
2. (at a race start) set
   Na mesta, pozor, sad! — On your marks, get set, go!

In everyday speech «pažnja» is more common; «pozor» is mostly used in commands and warnings.