Alter Aeon Online Help

Keywords are:  'thief skill listening'

Skill: listening                Lvl  9 Thie  (42%)
                                (obscure)   Requires: sneak
                                Group: Thief stealth skills

Usage:
listen
listen <direction>
listen <object>

The thief 'listening' skill allows a skilled thief to listen for and
hear if there are invisible or nearby enemies.  It can also be used to
tell if there are items inside a container or other object, though for
containers that can't be picked up or moved it is much harder to tell
what is inside them.

Note that some creatures and items are naturally very loud, while
others are naturally quieter.  Even a skilled thief may not always
hear everything.