The Detector - Energy is a block from the Railcraft mod. This block is meant to output a Redstone signal based on the type of Minecart that passes in front of it. The Detector - Energy will output a Redstone signal if any energy cart passes in front of it. Energy carts include the Batbox Cart, the MFE Cart, the MFSU Cart, and the CESU Cart. They can be placed under or beside Minecart Tracks, and will output a signal to the side that has a small square. When a Redstone signal is active this square will turn red.