The BLU-IR is a light source-receiver pair of photoelectric sensors used to turn on speakers in an adjacent room when a sliding door between the rooms is opened. The sensors are mounted on heavy duty aluminum brackets. The BLU-IR is a light source/receiver pair of infrared sensors for use with BSS Audio London Series Digital Signal Processors. They are used to sense whether doors or partitions are open or closed, so the mixer can provide audio to an overflow area.