Timer sounds an audible alarm after a set time, not to exceed 2 hours per caster level. You choose what type of alarm sound timer creates during casting and cannot thereafter change the sound’s basic character. Anyone within the area will hear the alarm sound clearly. Reduce the distance by 10 feet for each interposing closed door and by 20 feet for each substantial interposing wall. The sound lasts for 1 round. Creatures within a silence spell cannot hear the alarm.