This is a work-in-progress mod, but it's nearly complete. I still need to decide on final attribute values for the shields and who should spawn with them. Once that's finished, this will be available for download on the Nexus.

Energy Shields
This does not require a new game, but because of how different the game is with shields, I personally recommend you start a new game to get the full experience.

You've played tons of other games with recharging energy shields, and if you weren't at least curious about seeing them in New Vegas you wouldn't have clicked on this link. Maybe you want to give your character more resilience in combat, maybe you want a system that rewards use of cover, or maybe you just think it's freaking cool (it is). Well here you go. This mod adds new energy shields to the game, incorporating them fully into the whole world. They can be found in store inventories, as loot, and even from fallen enemies. Oh, you thought you were the only one getting this new power? Nope. Your enemies can now spawn with shields too. When equipped by others, shields carry the same effects as if you had equipped them, including any special properties, so watch out! You'll even see and (if close enough) hear their shields when you attack. Adding shields for both you and your enemies radically changes the way you fight and how you face each situation.

Shield units are equipped under your armor tab, and while equipped, they provide shield points to protect your health pool. Whenever you take health damage, the shield will buffer against it. As long as the shield holds, it also protects from limb damage and poison effects. Every time the shield is struck, there is a delay before it can start recharging again. Taking damage during this time resets the delay, so you need to break from combat to recharge. There is a bonus penalty added to the delay each time the shield breaks (0 SP). You can't view current shield points, but the system provides visual and audio cues to signal how well the shield is doing. It has a sound when charging from a delay, another for charging from a break, a sound for when it reaches maximum, and a warning for when your SP reaches 0. The shield also changes in color based on the percentage of health left. It starts blue-green at high health and slowly turns red-orange as SP drops. In order to useful without being annoying, the noises were specifically chosen to be loud enough without being too loud, and you'll only see your shield when you get hit. Several different shields with various properties exist, but only one can be equipped at any time. Shields use your earring slot, which was chosen because I couldn't find anything in the game that already used that slot.


Videos
Here are some videos of the mod in its beta stages to give you an idea of how it works. The first video is a very early beta from almost a month ago, while the second is more recent and much closer to how the shields currently function.
http://www.youtube.com/watch?v=BfVwlJxyWL4
http://www.youtube.com/watch?v=A-J0ttol6EY


Shield Guide
Rank is the shield's general level of power. Each rank is appropriate for a level range. The ranks are Buffer (1-5), Brace (6-10), Field (11-15), Ward (16-20), Wall (21-25), and Aegis (26-30). Enemies can't spawn with higher ranks until you grow in level, but some unique NPCs will have higher ranks at any time.

Max SP is the highest amount of shield points the shield can charge to. This represents the shield's total health. It fully absorbs damage on a breaking strike, so it can always protect against at least one attack. However, if any attack does more total damage than you have health remaining, your shield will critically fail and you will still die regardless of remaining SP (See FAQ "How does this work?" for an explanation).

Recharge is the number of SP recovered every second when charging. Getting behind cover is a great way to avoid attacks and recharge your shield. A higher recharge will let you more rapidly replenish shields so you spend less time in cover and more time fighting.

Delay is the number of seconds that must pass from you last taking damage before the shield begins to recharge again. You must stop taking damage or your shield can't ever recharge. Shields with a higher delay are weak against rapid attacks, which can quickly diminish your SP without leaving a chance for you to recover.

Break is the penalty in number of seconds that you must wait after hitting 0 SP before before shield points start recharging. Unlike Delay, which applies every time you take damage (including when at 0 SP), the Break penalty is only applied once each shield break. Shields with a higher Break are weak against strong single attacks, which can commonly break your shield and leave you vulnerable.



Conflicts
To be determined in final release. All playable and unique shields use the Earring equipment slot because I'm not aware of anything in the game that already does. If any other mod adds something in the Earring slot, you won't be able to equip that item at the same time as your shield.


(What I anticipate will be) frequently asked questions
Q: How does this work?
A: This system uses a new attribute called shield points. However, it's impossible to take damage to shield points directly. If NVSE ever gets event handlers and the AVMod functions that OBSE had, this may become possible (but FOSE never got them). For now though, I had to approximate it as closely as I could, and the method I use doesn't even require NVSE. When equipped, a shield constantly monitors the health of its user from frame to frame. If health ever drops, shield points drop and health goes back up a single frame after the damage was taken. There are checks to make sure it isn't free healing and checks to make sure it doesn't interfere with any healing you're doing. This is very similar to taking damage to SP, but it's not identical. Because the damage has still applied for one frame, a single attack powerful enough to kill the user will still do exactly that. Because HP damage is actually occurring first, all damage threshold and resistance effects apply as normal, so better armor makes a better shield. I would have liked to be able to negate the damage entirely so it doesn't even apply first, but again, this is simply not possible. What I've created is the best approximation available, and I'm quite happy with how it ended up. In the end, having shields "critically fail" against attacks higher than your current health isn't much of a problem, and you can even use it tactically when fighting shielded opponents.

Q: These have no DT. How do you know NPCs will equip them?
A: Every shield actually has 0.01 DT. You won't see this in-game and it won't have almost any effect, but it's still high enough that NPCs will always equip them whenever they evaluate their inventory items, because they'll have no better earring-slot items to equip. This lets me be sure NPCs who have shields will use them. Again, the earring slot isn't used by anything in the base game, but any mods you have that add earring-slot items may conflict with this.

Q: Aren't you worried about game canon?
A: Major groups like the Enclave, NCR, and Brotherhood have large-scale force field technology. It's not unreasonable that this could be miniaturized and made portable. I realize it's not within canon to add these to the game, but it's really not as far a stretch as you might think. I was careful to make sure shield assignments made sense based on factions. Some examples: Fiends have access to energy weapons, so it makes sense that they often spawn with shields. Brotherhood members are obsessed with technology, so they all have shields. NCR is able to afford to equip most soldiers with at least a basic shield, and Rangers always have one. Powder Gangers acquired some shields during their escape, so a few have them. Other than Caesar and Lanius, Caesar's Legion has technological restrictions and will not have shields. Robotic enemies all have at least basic shields present. Most creatures do not have shields, with only rare exceptions, such as bosses. My explanation for that is that their shields are psychically generated or something. Look, it's not without http://fallout.wikia.com/wiki/Psyker, and it makes for better boss fights. Just go with it.

Q: Will this slow down my game?
A: It shouldn't. My testing used areas with multiple shielded opponents, and I never saw a drop in frame rate. The script is actually not very complex and shouldn't cause any reduction in performance to run, even with a bunch of targets using shields at once.

Q: Does this protect my equipment from taking damage?
A: No. I simply felt this was too powerful, so I did not include it in the final version. Your equipment will still take damage from taking hits or using weapons. Likewise, you may still damage your enemy's weapon, which can be pretty useful considering your enemy's limbs are protected while shielded.

Q: Why do all the shields look like a Stealth Boy when I drop them?
A: I don't do modeling, so I'm not able to give them a unique appearance. Stealth Boys make a great stand-in for "general high-tech item." The shield units have no visual appearance when equipped, so you'd only ever see them by dropping them anyway. If someone wants to design a custom model and texture for them to use when dropped, I'd be happy to include it, but it's not a priority.

Q: Are you planning on adding a shield bar for the HUD?
A: I haven't done much with XML in several years, so creating a HUD element hasn't been in my ability since around high school. Instead, the shield has several different audio cues and changes color based on its health, so you still have a great indication of how it's doing in combat. However, I've already created two global variables for your current and max SP that are only updated when the shield is equipped by the player, so it should be possible to create a HUD element if someone wanted to do that. I personally can't, but at least I've made sure those who know how have the option.

Q: Why you'd make the enemies so much harder?
A: The addition of shields has a huge effect on gameplay and balance, but I've spent weeks getting the values to be what I felt was fair. If an enemy seems too hard, it may be using a shield with special properties, so try a different method of attack. If keeping damage on them to prevent shield regeneration is too hard, try using damage-over-time effects like flame weapons. Fire works wonders against shields. However, if you really feel that a certain enemy is simply unfair, please let me know.

Q: Will there be patches to add shields to enemies from DLC?
A: Almost certainly yes, and I'll be working on that. I own all current DLC, so I should be able to make these myself. It could take a little while though, because, due to making this mod, I've actually never played any of the DLC. I'll have to do that before I can appropriately balance any shields I add.

Q: Will there be patches to add shields to enemies from other mods?
A: For now, I'm going to leave that up to the makers of those mods (see Permissions below). You have to understand, I've been working on this thing for weeks just to get a version for the base game. Once I've already finished DLC patches, it's possible I may make patches for popular mods. I would really prefer if their creators did it, though. They'd know their own work better than me and would better be able to balance adding in shields. Adding the shields to existing creatures or loot lists is easy. Balancing these things is much harder. The work is really all in the planning, which I wouldn't have to do if someone who knew his/her own mod simply did it.

Q: Will this see expansions in the future?
A: There are currently no shield ranks appropriate for levels beyond 30. I may add those in later if they feel needed. There is also the potential for new shield classes. Besides those, there are tons of ideas that went through testing and were rejected for one reason or another, plus I may come up with other things. I'm not sure what I'll end up adding in the future.


Permissions
I didn't just design the shield system for this one mod. This is also a resource that I invite other modders to use. If you've got a mod that adds new creatures or NPCs, I'd love to see you create a compatibility patch that adds shields to them. I've built this system to be modular and it's honestly not very complex, so it's easy to add shields to new NPCs and creatures and even to create new available shields. I put a lot of time into getting this working and balanced within the game, and I'd love to see just how far it can go. Even if you don't want to make a patch to add in my shields, it should be pretty easy to adapt this system to whatever purpose you want. Actually, this mod originally started with the shield being added by a weapon and using your AP. I then switched to using a perk, and after that switched from AP to SP. The perk then went away in favor of shield items you crafted at a workbench. All versions up to that point only worked on the player, so the system has come a long way. I already have ideas for new features I may add later, but if you've got your own ideas and would like to use the underlying system in your own mod, please go ahead. I only ask that I receive credit with a link back to the download page and that I be told about it so I can see what you've made (I'm just curious). As with all of my mods, everything in the GECK can be found by filtering for my initials, KJK. This three-letter code isn't found on anything else, so it's a quick way to access just the new material.

Will there be a way to tell what kind of shield an opponent has (before killing them)?

Are there weapons that do bonus damage to shields (EX: pulse/emp)?

You said, "Whenever you take health damage, the shield will buffer against it." So, let's saying I'm using XFO's 0% DT passthrough mod. If someone shoots me for 10 damage, normally, my DT would absorb all of it. That is, there would be no health damage. In that case, would my shield's SP be affected at all by that attack, or does all damage come out of the shield first, then go to DT/DR?

I experimented with giving each shield class a different texture, but the appearance varies based on the armor/skin of whatever is using the shield, so that wasn't reliable. I also use color already to let you know the shield's health, so that's not an option. There just wasn't a good way to differentiate shield classes by appearance, so I didn't do that. To really know the enemy's shield type, you'll have to just attack it and see what works. I'd still of course like to add some indication, but I'm not sure what it could be.

Iron is more resistant to physical attacks and Insulated is more resistant to energy attacks, but nothing does bonus damage. To implement that would have required sticking a weakness on, which would affect how powerful a blow must be to kill you, thus I won't do that. Fire is really effective though. Damage over time effects (all fire are) beat the crap out of the shield to repeatedly reset the Delay time, thus never letting it recharge. You're immune to poison while SP remains, but watch out for other DoT effects.

If you don't take health damage, your shield won't activate and you won't lose SP. Actual health damage is calculated first, and all DT/DR act as normal. That's why you'll still see blood and you can die from any single attack higher than your current health. If you've changed the fMinDamMultiplier setting to 0, it should be possible to fully absorb hits and not even use the shield.

You could use an indicator in the player's HUD, something on/near the crosshairs maybe. That, or there could be some visible armor asset attached to the user that identifies that a shield is equipped, like a belt, halo, backpack, or something like that.

The way the shields works according to your description seems weird to me. I would think that the shield would always take damage first, then anything that penetrates would go to armor. I mean, the shield should extend outside the armor, not under it, right? The ablative armor is pretty useless for this reason. What's the point in being able to shrug off big damage if it's only possible when it doesn't exceed your max health? Anything that was going to one-shot you before will still be able to. As it stands, sniper rifles with sneak attach criticals can one-shot most humans pretty early on, and that won't change with the addition of shields. So, sneaky sniper types would end up with an even easier game with the addition of this mod.