Visible and hidden sentries are posted outside the imperial palace, with strict security.
Tips
memory
Two parallel pairs: 明岗 ('open post') + 暗哨 ('hidden sentry'). 明 (open/bright) and 暗 (hidden/dark) are paired opposites; 岗 and 哨 both mean guard posts. The whole layered defense in four characters.
usage
Almost always pairs with 戒备森严 ('tight security'). Used for VIP protection, military positions, and crime-novel surveillance setups, anywhere defenses come in visible and invisible layers.
