Alarm

When an alarm spell is cast, the wizard causes a selected area to react to the presence of any creature larger than a normal rat. The affected area can be a portal, a section of floor, stairs, etc. As soon as any creature enters the warded area, touches it, or otherwise contacts it without speaking a password established by the caster, the alarm spell lets out a loud ringing that can be heard clearly within a 60-foot radius, lasting for about a minute. Ethereal or astrally projected creatures do not trigger an alarm, but flying or levitating creatures, invisible creatures, or incorporeal or gaseous creatures do.

Note: This version of alarm originally appeared in the 2nd Edition Player's Handbook for Advanced Dungeons & Dragons from TSR. Its use here is for the purposes of providing context for the campaign only.