That was actually called the Caterwauling Charm, though. There’s another detection spell in DH: Hominem Revelio. The only known effects of this spell are (i) the ‘swooping sensation’ experienced by a detected person and (ii) the lack of any alarm when nobody is detected. It’s likely, however, that there is no alarm even when persons are detected; when it’s used against Harry, Ron, and Hermoine by Death Eaters there is no alarm mentioned in the text.
I’m fairly certain that’s how detection spells work though. In Deathly Hallows there were blaring alarms when the gang apparated into Hogsmead.
That was actually called the Caterwauling Charm, though. There’s another detection spell in DH: Hominem Revelio. The only known effects of this spell are (i) the ‘swooping sensation’ experienced by a detected person and (ii) the lack of any alarm when nobody is detected. It’s likely, however, that there is no alarm even when persons are detected; when it’s used against Harry, Ron, and Hermoine by Death Eaters there is no alarm mentioned in the text.