How do you lower your weapon in halo?

Answer 1

In Halo: CE (aka. Halo 1), look straight down. Your spartan will be looking straight forward with his weapon lowered.

In Halo 2, you must not be holding any grenades. Once you aren't holding any grenades, hold the button used to throw grenades (default LT). As long as you hold the button, your weapon will be lowered and you will no longer be able to use scopes on weapons.

In Halo 3, things are a little more complex. You must simultaneously press and hold the following buttons on your controller: LB, RB, up on the D-pad, A, and you must click and be holding the left thumbstick in. When you press these buttons, your spartan will jump. Once you land, your weapon should disappear from your screen and you should only see the crosshair from your weapon. If it didn't work, keep trying. Once your weapon is lowered, you can switch between the two weapons you're holding. If you shoot your weapon or melee, your spartan will raise the weapon again.