Features

The core idea of the mod is: when you draw your weapons, you equip your headgear. When you sheath your weapons, unequip your headgear.
"Headgear" is divided into three categories: helmets, hoods, and circlets. In the mod config menu (MCM) you can customize which of these you want to manage (taken off/on with the weapon state).
The default setup is that helmets and hoods are managed, circlets are not. This means that if you first equip a circlet, and then equip a helmet, when you draw your weapons, your helmet will be equipped, when you sheath your weapons the helmet gets unequipped and the circlet is re-equipped. Check the demo video to see this in action.

The player setting:
Three modes are available for the player: Auto, Enabled, and Disabled.
"Enabled" means the mod immediately applies to any headgear you equip. This of course means if you equip it while weapons are sheathed, the headgear will get immediately unequipped.
"Disabled" means, well, disabled, the mod doesn't do anything for the player.
The "Auto" setting (which is the default) is aimed at players who might want some of their headgear displayed at all times, without visiting menus to toggle between Enabled/Disabled. In this setting, if you equip a headgear while your weapons are drawn, the mod will start managing it. (When you sheath, the headgear will get unequipped). However, if you equip a headgear while your weapons are sheathed, the mod will not manage it, it will stay on at all times.
Why is this good? Let's suppose for most helmets you want the mod to take them off/on. So you equip them while weapons are drawn. But then as you progress you receive a stunning looking helmet that's open faced etc. and you want it on at all times. Equip it while weapons sheathed. It will be not be touched by the mod. Then you progress, get a better helmet, but you want the mod to manage it. Equip it while weapons drawn. And so on, and you did not have to visit a single menu/setting.
But if you know you'll want the mod to manage every helmet you own, better set the player setting to "Enabled".

Followers:
If enabled in the MCM (default yes), the mod will work for all followers, both vanilla and modded ones. When they draw their weapons, they will equip the headgear in their inventory that has the best armor rating, and passes the MCM's armor conditions.
When they sheath their weapons, they will unequip this helmet, and will retain the MCM's not managed armors (such as circlets in the video example), and will also retain worn wigs.

All NPC:
There is an option in the MCM to enable the feature for all NPC in the game. Be careful with this setting. It is there experimentally, and has not been extensively tested. When enabled all NPCs will unequip their helmets, and only put it back on when they draw their weapons.
There is an option to exclude guards when enabling for all NPCs - this allows guards to keep their helmets on at all times.

Bad weather:
If this is turned on, the player and enabled NPCs will equip their helmet if it is raining/snowing.
You can of course manually unequip your helmet.


Plugin info:
The plugin is ESP-FE and does not count towards the regular esp plugin limit.
The mod should work with all game versions. (1.5.97, 1.6.x)

A demo video of the core features:



Requirements
- SKSE64: Hard requirement. Make sure you get the version that is compatible with your game version.
- SkyUI: Hard requirement. (Not just for the MCM, the mod won't function properly without SkyUI!)
- Spell Perk Item Distributor (SPID): Semi-hard requirement. Necessary to make the mod function for followers/other NPC, it won't work without this.
- Keyword Item Distributor (KID): Semi-hard requirement. Necessary to make wigs work, and to patch for other mods that add items that may be otherwise misidentified. (Necessary for example for KS SMP Wigs, and JS Armored Circlets).
The plugin is ESL flagged and was made with the latest Creation Kit. If you play on a game version earlier than 1.6.1130, you might need Backported Extended ESL Support.



Installation
Recommended way: with your favorite mod manager, I recommend vortex.
Manually: extract the contents of the zip archive to your Skyrim Special Edition\Data folder.


Uninstallation
Not recommended in Skyrim modding. If you decide to remove it from a saved game, you're on your own with any issues.


Compatibility:
Not compatible with other mods that implement the same feature of equipping-unequipping / showing-hiding headgear.
Should be compatible with everything else.

Wigs from other mods are recognized by using KID to distribute keywords to them. It is highly likely I missed many of the mods that exist in the wild out there and and wigs. Let me know, and the list can get updated.
While the mod should work out of the box for mod-added armors, if it doesn't have the necessary keywords, then it also needs to get a treatment through KID. Let me know if you find misbehaving headgear.



Why choose this mod? Why not to choose this mod?
There are many other mods that already implement a similar feature, such as Equipment Toggle 2, Helmet Toggle 2, etc. So what are the differences?

With my approach, Immersive Headgear Manager can mix between headgear types, and can manage the enabled ones depending on weapon-state, and can retain the others after the managed one is unequipped. It can also differentiate between modded wigs and headgear, and can do it seamlessly for followers as well. As far as I am aware, this mod is the only one that can do this currently. And it can all be customized in an MCM, no need to edit jsons or ini files.

On the other hand, my mod contains features done with papyrus scripts, which are an inferior implementation regarding execution performance. For example, when enabled for followers, the equipping and unequipping of the helmet can get noticeably slow if their inventory is large. I have mitigated this issue by implementing a caching system, but when you give an NPC a new helmet, the script needs to loop the inventory to find it, thus they might take a few seconds at first when they have to equip it. You can compare this in the demo video: on the scene with Lydia, all gear (the helmet, the wig and the circlet) are cached, and she equips them almost instantaneously, in sync with the player. On the Serana scene however, I just gave her the circlet before recording, so while she immediately equips the helmet, she takes almost 3-4 seconds to unequip it while looking for the circlet. Again, this lag only happens on first time equips.
Another consideration, is that my mod actually equips and unequips these items (unlike the previously mentioned mods that hide them with SKSE or Dynamic Armor Variants).
Wait... scripts? So will this mod make your PC have a heart... umm... CPU-attack and explode? Of course not. If your game is stable, this mod won't affect its performance in any noticeable way. But understand that it is one more grain added to your vast collection of mods that uses scripts (some of which probably use much more taxing and less optimized scripts), adding tasks to Skyrim's finite-resourced papyrus stacks.

To sum up (TL;DR): the selling points of my mod are that it can leave given types of headgear on while managing others, this same feature works for followers, some changes don't require you to spend menu time, and it does not require IED/FNIS/Nemesis/Pandora/other black magic(kidding).
If you'd prefer another approach with different highlights, there are other nice mods to choose from. If you want something with even more complex settings and an animation, I recommend Helmet Toggle 2 (though I personally haven't tried it), or if you want an ultra-efficient SKSE dll implementation and don't mind editing jsons to change your settings, I recommend Equipment Toggle 2 (which I did try and have used for a while).



Legendary Edition? Console ports?
I am no longer releasing mods for Skyrim LE. My recommendation for LE users is Auto Unequip Helmet LE, which works for the player only and uses a similar approach to my mod.
Due to the SKSE requirement, it is not possible to port this to consoles.




- ... which Serana replacer in the video and on the screenshots?