Harry Potter - Secrets of Hogwarts

You set an alarm to emit a piercing shriek when an unauthorized person enters the area. Until the spell ends, an alarm sounds whenever a Tiny or larger creature touches or enters the warded area. When you cast the spell, you can designate creatures or areas within the hemisphere that won't set off the alarm. The alarm produces an unpleasant screaming sound for as long as the intruding creature is in the area of the spell, audible from as far away as 300 feet.