1. Listening at doors includes like activity at other portals such as
windows. It is accomplished by moving silently to the door and
pressing an ear against it to detect sound.
 
 
Pick Pockets Open Locks Finding and Removing Traps Setting Traps Moving Silently
Hiding in Shadows Hear Noises - Climbing Walls Back Stabbing
The Thief Listening At Doors - Dragon magazine 1e AD&D


Hearing Noise is simply listening intently.

The thief and his or her
accomplices must themselves be quiet (but not silent as in moving). This
function can be repeated as often as desired. It requires a full minute to
listen, i.e. one-tenth of a normal turn, or time equal to a melee round.
Note that sleeping creatures, undead, and many other creatures do not
make sounds discernible through a portal. Success informs the hearer that
someone or something awaits beyond the portal. (DMG)


 

Q: Is the thief's hear noise ability
continuous, or does it require concentration?
Is the ability strictly
limited to listening at doorways?

A: The hear noise ability is neither automatic
nor continuous. The thief must
quietly concentrate on hearing noise; if he
is wearing a helmet, he must take it off. A
thief is not limited to listening at doors; he
can hear faint sounds from any source.
(142.10)


DMG:

Hearing Noise:
This is pretty straightforward.
The thief, just as any other character,
must take off helmet or other obstructing headgear in order to press his or her ear to the door surface in order to hear beyond.

see Listening at Doors +
see Hearing Noise +


LTH (d47, bd3)
The chance to hear noises assumes
that the area is quiet. If the party is talking or moving about, this action will negate the chance. Hearing a sound can
also involve discerning what is heard —
but this ability does take thief’s training.
Reroll (at the same chance as to hear a
noise) to see if the sound was discerned
as to what a likely source or cause might
have been. Discerning a noise might not
only mean hearing bits of actual conversation, but might also allow a guess as to
how many persons are engaged in speaking. The DM should not give away too
much!

Obviously, non-thieves can hear things,
but the ability of discernment should not
be allowed to them. Give other characters 1/2 of a thief’s chance (by level) to
hear noises, but avoid a procession of
1 character after the other going to the
door to listen! Such a procession might
be heard from the other side. Note that
Undead rarely make noise.