Spot/Listen in Combat

[DarkEternal]

Players love to use Invisibility. All kinds of Invisibility, and at greater levels, Great Invisibility is great if they are fighting against incredibly powerful beasts that alas, lack the ability to cast Purge Invisibility or True Seeing.

These beasties, however, usually have a high Listen-Spot skill, and I was wondering how it worked.

For instance, let us say George the Cleric used Greater Invisibility from a scroll, or it's his domain or something. He's now effectively can not be found, by any means necessary by said beast except with said skills.

How do you roll them? I remember, vaguely, reading in the Rules Compendium that you can, one per round roll a Listen or Spot check(or both of them?) to see/hear where the enemy is. The invisible creature gets a +20 to his skill modifier and if you beat the result by 10 or something, you know the exact spot the invisible character is, right?

Now, my question is, what sort of action is it? Immediate, Standard, Free on your turn?

And more importantly, once you beat the check, once you have a fantastic Spot modifier and you beat it by the necessary amount, do you see said person only for that round before he moves away, or is it like you purged his invisibility for the reminder of the encounter? I am aware that the miss modifiers are still the same, even when you know the exact square, just wondering about the longetivity of the check.

Even more for making a Listen check that exceeds the one necessary(think that one is by 20 or something) to know where exactly he is. Some sort of logic would dictate, that the moment the person moves out of the square, you lose the ability to know where he is now and have to make a new check or something?

[SurlySeraph]

Every time you have a chance to spot something in a reactive manner you can make a Spot check without using an action. Trying to spot something you failed to see previously is a move action.

Listen gets much the same wording.

I believe you remain aware of the creature until it makes a new Hide check (or MS check, for Listen) that you fail to beat.

[Saph]

Most of your answers can be found here - SRD: Special Abilities: Invisibility (http://www.d20srd.org/srd/specialAbilities.htm#invisibility). An invisible creature can be spotted with a DC 20-40 Spot check, or 40-60 if you want to pinpoint its location. This is usually too high to be practical.

Listening for an invisble creature is much easier. DCs are listed in the above link - note that the DC to hear an invisibile creature in combat or speaking/spellcasting is 0. The listener gets a reactive Listen check every time the invisible creature makes noise (see the Listen description (http://www.d20srd.org/srd/skills/listen.htm)), which probably translates to every turn when it takes actions. Since it's reactive, it's a free action. Beating the DC by +20 pinpoints the target's location.

So every combat round the listening creature gets a flat DC 0 Listen check, and if it hits 20 it gets to pinpoint the invisible creature's square (which most monsters can manage fairly consistently). Note that pinpointing the square is not the same as seeing it - the invisible creature still gets a 50% miss chance and all the other benefits of invisibility - but it's more than enough to, say, drop an AoE on the thing.

Invisibility is thus a powerful combat buff (as you'd expect) but it's far from an auto-win button.

[DarkEternal]

I see, so basically, Listen is much more viable then spot, and you always hear(well, if it's a person wearing plate or a wizard casting a spell if he doesn't have certain feats) from what general direction the spell comes, but you have to beat the check by +20 against their Move Silently modifier to pinpoint the exact location and you can do that as a free action every turn? Alright, just hate it when I get blasted constantly by an entire invisible party with no way to strike back.

[Saph]

Yep, except that if they're actually in combat and attacking the thing, the DC to hear them is only 0. You also get a separate check against every invisible opponent.

Once the fight gets into melee I usually rule that if something is actually hitting you, you know where it is. This is partly common sense (it's not hard to figure out where an invisible thing is when it's repeatedly stabbing you through the chest) and partly to speed up play (rolling multiple Listen checks every turn gets old fast).

[DarkEternal]

I understand. They still make a Move Silently check(if they are a class that does not have that skill at all, they roll it with a Dex modifier bonus for the result, minus all armor check penalties), and I need to beat the result by 20 to know where they are, exactly. Grand.

No more sodding clerics using their magical teeth to turn invisible for me!

[Curmudgeon]

Trying to hear something you failed to hear previously is a move action.
Trying to spot something you failed to see previously is a move action. The combat use ambiguity mostly comes from this single word. With Listen the "something" is usually interpreted as the same noise, so a creature making a different noise would permit a reactive (no action) check. With Spot the "something" could be as narrow as the same creature in the same location performing the same action, or as broad as simply that same creature. Which could mean that you'll never get a new check without using a move action.

Check with your DM; YMMV.

[ericgrau]

This is what you want:
http://www.d20srd.org/srd/specialAbilities.htm#invisibility

The DC for most things done by an active PC (casting, attacking, etc.) is listen DC 0 or spot DC 20. That lets the monster notice the PC's presence and gives a rough direction. For an exact square add 20 to the DC, but even if you attack the right square there is still a 50% miss chance.

Other common ways to handle invisibility are flour bombs, leaving flour or another material on the floor, blind fight (+listen), see invisibility (lasts a couple hours, good buff before assaulting someone), invisibility purge and glitterdust, but only after you find the guy's square using another method.

Intelligent and experienced high level monsters in general should prepare for invisibility, scrying and other divinations (lots of abjurations for those), teleportation (e.g., dimensional anchor/lock), other detectable magic (it's a cantrip man, use it), breaking down conjured barriers, casting in general (silence is infamous, but there are 30+ other methods), etc. Don't start picking on your PCs' tactics specifically unless the monsters know the PCs, but do make general preparations.