If a NPC falls, and no one is around to hear it, does it make a sound?
According to Bethesda: Yes. Yes it does. And you will be punished for it.

Mod Overview
Fixes NPCs magically detecting the player after a stealth kill as well as other detection issues. See the video above for an example where a fully perked, master sneak is detected by sleeping NPCs.

Why does this bug occur? (More Below)

All of the condition logic in this mod is handled natively (not via Papyrus), making it extremely responsive and lightweight. Additionally, no vanilla records were edited, making it highly compatible.

The mod currently includes five fixes. All are optional. You can pick and choose which to enable in the MCM Menu.

🐛 Bug: Sleeping NPCs can detect unobserved stealth kills and vampire feeding, resulting in bounties or combat.
✅ Fix: Sleeping NPC Detection Fix
Sleeping NPCs will now only react to the player or enemy NPCs, not Detection Events. A successful sneak kill or vampire drain on a nearby NPC won’t wake up other sleeping NPCs.
As in vanilla, they can still wake up if:

• You move too quickly near them
• You aren’t sneaking
• You fail to kill an ally with a sneak attack
  

Tweaks to the Sleeping NPCs Fix are available in the MCM Menu.
🐛 Bug: All NPCs in a dungeon can become alert after a single stealth kill—even when no one witnessed or heard it.
✅ Fix: Stealth Kill Fix
When you land a successful stealth kill with a silent melee weapon (e.g., a dagger), nearby NPCs who:

• Aren't looking in the player's direction, and
• Are more than ~6 feet (1.8 meters) away
  

…will not automatically detect you. This prevents an entire dungeon from being alerted by a single unobserved kill.
However, if another NPC is looking in the direction of the kill, they may still go on alert—even if you remain undetected—just like in vanilla behavior.
Tweaks to make the "Stealth Kill Fix" have less restrictions are available in the MCM Menu.
🐛 Bug:  Even if fully undetected and completely behind their target, players' (supposedly) silent attacks are able to alert NPCs mid-swing before the weapon swung actually makes contact, resulting in no stealth bonus damage.
✅ Fix: Attack Detection Fix
If the player was undetected for at least ~2 seconds prior to attacking—and is wielding a silent weapon—they cannot be detected during the attack animation itself. Detection checks resume as normal immediately when the attack hits.

• Note: For bows, this fix only covers the 'release' portion of the drawing animation and only turns on if the player is not moving while shooting and while no enemies are looking in your direction. Tweaks to make the Attack Detection Fix have less restrictions are available in the MCM menu.
  

🐛 Bug: Sneaking with spells equipped increases your chance of being detected—even if you’re not casting them. This happens because spells emit light just by being equipped, which NPCs can detect.
✅ Fix: Sneak Spell Light Fix
While sneaking, spells no longer emit light just by being equipped. See Gif Below. Light emitted while standing or actually casting remains unchanged.

• Requires Light Placer.
• The included plugin was generated using my Synthesis patcher, Disable Spell Light Emission and was only run on the base game plus the official DLCs.
• If you want the fix to apply to ALL spells in your load order (and not just vanilla ones), run the Synthesis patcher itself instead of using the prebuilt "Sneak Spell Light Fix" file.
• If going that route, ensure the patcher created a .esp (which you should enable) as well as a file called, "disableSpellLightPatcher.json" in the "LightPlacer" folder.
  

🐛 Bug: Player is detected during a killmove—even though if they had attacked normally (without a killmove going off) they wouldn’t have been detected.
✅ Fix: Killmove Detection Fix
During a stealth killmove, nearby NPCs are temporarily blinded, preventing them from seeing the player during the animation. (They can still detect the sound of the hit itself during the killmove).

• Essentially, if you would have remained undetected without the killmove, this fix ensures you stay undetected with the killmove.
  

MCM Menu Tweaks:

Requirements
SPID
MCM Helper
powerofthree's Papyrus Extender
Scrambled Bugs (or  Poached Bugs VR , if using VR) with Perk Entry Points: Apply Multiple Spell = true in ScrabledBugs.json. (If you use Requiem, this is already set to true).

Note: You only need Scrambled Bugs if you are using the "Stealth Kill Fix". If you are only using the sleep fix, you don't need it.

Compatibility
Should be compatible with all mods, stealth settings are not directly affected. No vanilla records have been modified.

Installation
Ensure you have all the requirements and install with your preferred mod manager. Position in Load Order is irrelevant.

Which fixes should you enable?
Generally, I'd recommend most of the fixes as they are direct improvements over the vanilla interactions. 
The only one that is more of a subjective change is the "Stealth Kill Fix".

• Some people like the balance of only being able to do a single stealth kill per encounter (since they magically get detected right after it).
• To others, that's annoying and unfair.
• So whether you install that module is up to what kind of balance you prefer. 
• The Stealth Kill Fix can make stealth easier in some respects, so be aware of that.
  

Future Plans:

• A "not a bug but a feature mode" where my fixes are chanced/skill based for those who would want that.
  

My other Mods:

Requiem-Related Mods:

Requiem - Auto NPC Patcher -  Makes any mod playable in Requiem. A Synthesis Patcher and SPID configuration that adjusts the stats, perks, and levels of NPCs added by any mod to be in line with Requiem's Balancing.

 Requiem - Unofficial Reqtificator Lite - My recreation of the Reqtificator in Synthesis. Allows you to get over the 254 master limit easily.

My Requiem Patches:
Requiem - Reqtificator 254 Master Limit Workaround - xEdit and Mod Organizer
Requiem - Ryn's Mehrunes Dagon's Shrine
Requiem - Vampire Armor Expansion - Vampire Clothing Expansion

Attacko's Daedra Integration and Rebalance Series - COMPATIBLE WITH REQUIEM - My series of mods that rebalances and integrates Attacko's Daedra into the world in a lore-friendly way.
Abhorrent Behemoth • Anthropoid Daedroth • Bipedal Charyboid • Fire-Tounged Daedroths • Sulking Twilight