unannounced

un- +‎ announced

unannounced (not comparable)

1. Not announced beforehand.
   • 2015 April 15, Jonathan Martin, “For a Clinton, It’s Not Hard to Be Humble in an Effort to Regain Power”, in The New York Times‎:

     In 2008, she was at times criticized for being detached from voters, insulated in a bubble of staff and security and avoiding spontaneity. She began her 2016 campaign by riding 16 hours in a van from New York to Iowa, making unannounced stops at gas stations and fast-food restaurants, before arriving for what was billed as a series of low-key conversations with a handful of voters.