Note: There are two versions of the led collar. 1.USB Charging Version Charging once the light gets weaker will help to improve the service life of the battery 2.Button Battery Version Replace the button battery when power off CR2016 Button battery x 2 pcs Please choose the version you want. specifications Width Neck Circumference XS 2.0 cm 28 - 40 cm/11 -15 inch S 2.5 cm 35 - 43 cm/13 -16 inch M 2.5 cm 40 - 48 cm/16 - 18 inch L 2.5 cm 45 - 52 cm/18 - 20 inch XL 2.5 cm 52 - 60 cm/20 - 23 inch Feature: Three flash Mode First Click_Quick Flash Second Click_Slow Flash Third Click_Steady Light