Simple Q&A D&D 3.5 (by RAW) XXII

[mattie_p]

A 363: Activation varies depending on the special ability. For example:

Light Generation
Fully 30% of magic weapons shed light equivalent to a light spell (bright light in a 20-foot radius, shadowy light in a 40-foot radius). These glowing weapons are quite obviously magical. Such a weapon can’t be concealed when drawn, nor can its light be shut off.

Activation
Usually a character benefits from a magic weapon in the same way a character benefits from a mundane weapon—by attacking with it. If a weapon has a special ability that the user needs to activate then the user usually needs to utter a command word (a standard action).

Defending
A defending weapon allows the wielder to transfer some or all of the sword’s enhancement bonus to his AC as a bonus that stacks with all others. As a free action, the wielder chooses how to allocate the weapon’s enhancement bonus at the start of his turn before using the weapon, and the effect to AC lasts until his next turn.

A warning weapon grants you a +5 insight bonus on initiative checks as long as it is held.

The blade also has a special sunlight power. Once per day, the wielder can swing the blade vigorously above her head while speaking a command word.

Light, One-Handed, and Two-Handed Melee Weapons
This designation is a measure of how much effort it takes to wield a weapon in combat. It indicates whether a melee weapon, when wielded by a character of the weapon’s size category, is considered a light weapon, a one-handed weapon, or a two-handed weapon.

So some may merely be held (warning, light generation) in order to activate, some require the weapon to be wielded appropriately.