Press the battery pack on the Happy Birthday Necklace to activate the lights. Choose from three light functions. LED Functions: Fast Flashing, Slow Flashing, Still Light. LED Colors: White Dimensions: Diameter: 1.68 in. Necklace Lanyard: 21 in. Batteries: Includes 2 Replaceable Batteries, we do not carry the replacement batteries. Packaging: Retail ready, individual poly bags, 25 pieces per inner bag – 250 pieces per carton.