Thank you for viewing! This is a light-up collar that allows you to walk your dog safely even at night. Color: Blue Size: XS (approximately 10cm when measured) *Other sizes are available, but they need to be ordered, so please inquire in advance. Battery operated. There is a button, and when you press it, the collar lights up and glows blue, or can be set to blink. It's very noticeable at night, so you can be sure to walk your dog safely.