I can't use any sound or vibration because it will wake my wife. I put my mobile by the side of the bed facing me and cover the "speaker" with tape. When the alarm goes off a light comes on. This light is bright enough to wake me, but not my wife. Have only used it to wake up for WBTB but will experiment with different brightness (basically covering part of the mobile's display) for DEILD attempts, CAN-WILD and EILD.