Detector Rails are used in sending out a signal through redstone wire to activate another object like a note block. To craft one you need iron ingots on the sides, a stone pressure plate in the center and redstone dust in the bottom center.
Detector Rails
Minecraft Discussion
Minecraft Crafting
Blocks
Ore Blocks TNT Wool Glowstone Stairs Slabs Clay Block Snow Block Brick (Block) Bookshelf Stone Brick Sandstone Smooth Sandstone Jack-O-Lantern
Mechanism
Pressure Plates Doors Trapdoor Stone Button Redstone Torches Note Block Lever Jukebox Redstone Repeater Dispenser Redstone Lamp Pistons Alternate Income
Tools
Shovel Hoe Axe Pickaxe Bucket Flint and Steel Fishing Rod Clock Map Compass Fire Charge Shears
Challenges
Careers Light Grey Grey Rose Red Dye / Red Wool Orange Dandelion Yellow Dye / Yellow Wool Expansion Packs Light Blue Cyan Purple Pink Magenta Green Wool Blue Wool Brown Wool
Misc
Painting Sign Ladder Iron Bars Glass Pane Paper Book Bed Fences Fence Gate Eye of Ender
Food
Bread Sugar Cake Cookie Bowl Mushroom Stew Golden Apple Melon Block Melon Seeds Pumpkin Seeds
Enchantment and Brewing
Glass Bottle Cauldron Brewing Stand Magma Cream Blaze Powder Gold Nugget Glistering Melon Fermented Spider Eye Enchantment Table
Transportation
Minecart Powered Minecart Storage Minecart Rails Powered Rails Detector Rails Boat
Basic
Sticks Torches Wooden Planks Furnace Crafting Table Chest
Armor
Helmet Leggings Chestplate Boots
