To turn on simply push in the knob located on the battery pack. Press knob again to turn on the flashing function. Diameter (when stretched): 2.5 in, 6.35 cm - LED Colors: 3 White Note: Although we try to use the best white LEDs available, the tone of the white LEDs will vary quite a bit from unit to unit. The shades of white are inconsistent; some appear more bluish than others. Batteries: Includes 2 replaceable AG10 batteries. - Weight: 0.09 LB