Adjustable Flashing Nylon Pet Dog Safety Collar with LED Lights Blue XL Extra Large Size (XL) Walk Your Pet Safely and Be Seen! The Item have three modes:1.Steady On 2.fast flash 3.normal flash 100% Brand New and high quality How to measure your dog's neck size: measure around the neck close to the shoulder and allow room for a comfortable fit. Must-have safety collar helps incoming cars and traffic see both you and your pet in the dark.