Items and equipment will only "ping" on Detect Alignment spells if they have a special aura that says so. Like a Nine Lives Stealer.
has the power to draw the life force from an opponent. It can do this nine times before the ability is lost. At that point, the sword becomes a simple +2 longsword (with a faint evil aura).
But even so, only after it has stolen nine lives, until then, it has a strong Necromantic aura, which is neither good or evil.
The Holy Avenger, for instance, despite being the iconic paladin sacred sword, does not emanate a Good aura because it only shows it's special powers in the hands of a paladin, otherwise it's a simple +2 magical longsword made of cold iron.
But, if the item is said to have a certain aligment, like being good-aligned from Holy enchantment or evil-aligned from Unholy, then it will also show with the corresponding aura, as per Detect Aligment spell description, but only if the caster level is 5 or higher. This is also the case for a Holy Avenger being wielded by a paladin, which gets the Holy enchantment and becomes good-aligned.
Artifacts sometimes will have auras that are different from regular magic items, and will state so on their Aura field, like the Book of the Damned
Aura overwhelming all schools [chaotic, lawful, evil];