From Longman Dictionary of Contemporary Englishunannouncedun‧an‧nounced /ˌʌnəˈnaʊnst◂/ adjective, adverb EXPECThappening without anyone expecting or knowing about it We arrived unannounced.
Examples from the Corpus
unannounced• My brother is famous for showing up at our houses unannounced, usually around dinner time.• an unannounced visit• Investigators from the health department made unannounced visits to the hospital in March. 