What has an "aura" for the purpose of Detect [Alignment] spells?

Question

A buddy of mine said something about only certain types of creatures/characters (such as outsiders, alignment subtypes, and divine/profane classes) generate an "aura" for the purpose of Detect [Alignment] spells, thus, most normal characters wouldn't show up on Detect [Alignment] at all. Is this true? There is an aura gauge for "creatures", and by definition "creature" should include every type of character.

PHB pg306 creature: A living or otherwise active being, not an object. The terms "creature" and "character" are sometimes used interchangeably.

So, in the end, Detect [Alignment] spells should reveal a matching alignment aura on even a standard Human Fighter if their alignment matches the spell correct?

Edit: After reading and discussing these answers and after discussing the definition of a "creature" with my friend he is now under the impression that he was confusing it with 2e rulings.

Answer 1

The rules indicate that everything that isn't true neutral has at least a "faint" aura matching with it's alignment (though I'd argue that faint auras are not a big deal and not very noticeable unless many overlap) and that specific circumstances need to be met in order to show up more strongly on alignment-detection effects.

From what I gather, the rules for properly showing up are as follows:

• Any creature that does not meet the requirements below, but has high enough HD (minimum 11 HD for an aura stronger than faint).
• Outsiders have an aura that matches their alignment (min. 2 HD for aura stronger than faint).
• Undead have an aura that matches their alignment, except for good ones, because according to RAW undead cannot be good (min. 3 HD for aura stronger than faint).
• Clerics have an aura corresponding to the alignment of their deity (except for clerics of true neutral deities or godless clerics who do not take an alignment-based domain), min. class level 2 for aura stronger than faint.
• Anyone enchanted with magical effects that are clearly aligned in some way will radiate that spell effect's alignment (min. casterlevel 3 for aura stronger than faint).
• Anyone sufficiently covered in magical items that are aligned will seem to radiate that aligment (probably only the case with aligned full-plate armor, otherwise it should be easy to tell that the aura does not originate from the person themselves), min casterlevel 3 for aura stronger than faint.

It is also specifically mentioned that

Animals, traps, poisons, and other potential perils are not evil/good/lawful/chaotic, and as such this spell does not detect them.

which should mean that all entities of animal intelligence or lower cannot be detected (should be obvious considering that any alignment other than true neutral requires a certain level of intelligence to make sense), unless they specifically meet any of the criteria mentioned above.

Answer 2

Detect [Alignment] will detect any creatures of a particular alignment.

What your friend is likely confused about is the Aura Strength mechanic. Creatures like Clerics and Demons have a stronger aligned aura will detect as if they are stronger than a normal aligned creature would. Basically, creatures with a particular alignment that don't have any particular connection to that alignment have a weaker aura that creatures that have a stronger connection. For example, an evil level 11 Human Rogue would have a Moderate aura of evil, while a 2 HD Dretch would have the same aura strength.

This is all spelled out in the spell description, along with a table that maps each type of creature to the various requirements for each aura strength category.