Minecraft wiki entry for detectredstone, associated text: Specifies the direction of Agent to detect a redstone signal.
Must be one of:
forward to detect the block on the front.
back to detect the block on the back.
left to detect the block on the left-hand side.
right to detect the block on the right-hand side.
up to detect the block on the top-hand side.
down to detect the block on the bottom-hand side.