Sometimes we internalize years of rules that it becomes hard to explain on the fly. Recently, there's been a lot of questions around the idea of surprise and stealth. I've taken the time to spell it out for how I rule things citing the AD&D rules where at all possible, explaining reasons when not.
There's not a lot in hard, fast, or concise rules in AD&D but some can certainly be extrapolated. A few items are because I wanted to codify how some scenarios played out for transparency.
Surprise (meaning to engage in combat in any way) standards apply. Rushing into a room of monsters where they are unaware calls for surprise.
- Surprise is not stealth.
- Surprise circumvents stealth when the attack is initiated.
- Surprise can only be attempted outside of hearing range.
- Random Encounter surprise distance will be 1"-3". YMMV for planted encounters.
- Surprise checks starts the moment the surprised party could be aware of the opposition (line and direction of sight, as well as sound).
- Undetected (stealth, invisible) Surprise Chance is 4-in-6 (PHB103, MM39 "Elves")
Sneaking with Move Silently
If you can hear an alert monster, they will hear you if you fail to move silently within certain distance.
- All distances are as the Ghost flies.
- Provided that they are intact and the walls are of standard thickness, doors HALVE the ranges below (my rule).
- Loud noises DOUBLE the range (my rule). (sounds of battle, chopping down a door, chipping away a brick wall)
- Unalert HALVE the ranges. (distracted, sleeping, eating, bickering over dice, etc)
- Overwhelming noise halve the ranges. (active mining, a loud thunderstorm with a downpour of rain, etc)
- Rangers enjoy 60' for metal armor due to facilitating their surprise.
- The below distances are based on a pursuer listening for someone, which is equivalent to monsters being alert (DMG68).
- Given the above, characters in metal armor moving cautiously (1/10th movement, PHB102) can be heard at 60 feet, 30 feet for rangers.
- The below section under NOISE is extrapolated to loud, normal, and quiet noises(my rules).
- Spellcasting and normal conversation is normal (my rule).
- Loud noise always puts monsters on alert at best, gets them to come investigate at worst.
- This applies to monsters.
- Detect Noise, spending the time and a successful role could give the approximate distance.
- A solid room (walls a few feet thick, intact, enclosed) with solid closed doors, but loud noises would balance out. (example: hammering away at a brick wall in a closed chamber is monster-audible for 90 feet. Open the door, because you're a prankster who hates your friends, and it's 180 feet).
- A solid room with solid closed doors in the middle of an active slave-mine where pick axes and mine carts and making a ton of noise will bring the range of two fighters in a battle with two gnolls in half twice (90 to 45 to 22.5 feet). The guard station 40 feet away won't hear it, unless someone swings open the door.
- An open door in a giant quiet crypt chamber, while adventures are chipping off mineral build up, with hammers and chisels, off of a big sarcophagus is going to be 180'.
- A magic-user casts invisibility in a closed room can be heard 30 feet away.
Really Drawn Out Examples
Situation A: A fight breaks out with oil bottles shattering, zombies being lit on fire and the frenzied snarling zombies ripping vines out of the wall to free themselves (this is sounds of battle). Small monsters to the north are busy feeding a big monster. I'm going to call shattering glass alone on the same level as loud, which means they are now on alert from 90'.
|Red guy heard zombie violence only 55 - 60 feet away.|
Situation B: A bunch of noise just came from the south. The monsters are in a depression in a big cavern excitedly communicating with each other over what they just heard. One of the monsters towers up over the edge giving it only a quick roll of the eyes or turn of the head to see what made the noise.
|Red monster is alert.|
A thief needs to get about 10 feet closer than 30 feet to look at the edge to get the information he is after because of line of sight. He makes his intentions known and says he is going to move silently. A character in leather armor (so relatively quiet) makes a move silently roll as they creep forward to look over the edge of the pit.
|Damn it, geometry!|
Surprise is checked at this point, fairly.
Situation G: The elf assassin, peering around a statue, sees a ghoul up ahead. 40', sniffing the air and peering around in the hallway.