XS number: suitable for neck circumference 28-38cm, width 2.0cm, total length 41cm, weight 37g, using 2 CR2032 batteries

Size S: Suitable for neck circumference 34-41cm, width 2.5cm, length 44cm, weight 50g, using 2 CR2032 batteries

Size M: Suitable for neck circumference 37-46cm, width 2.5cm, length 50cm, weight 56g, using 2 CR2032 batteries

Size L: Suitable for neck circumference 41-52cm, width 2.5cm, length 56cm, weight 58g, using 2 CR2032 batteries