The collars came quickly. We have had them a week. They are easy to program. They fit our 12-pound dogs. THEY ARE UNBELIEVABLY EFFECTIVE!!!!! Our terrier mix and our Chihuahua were starting to bark so much at other dogs during walks that we didn't enjoy walking them anymore. We tried a human dog trainer, a sonic trainer, a squirt bottle, bitter apple spray, water balloons, a gentle leader, yelling, pleading, ignoring. A friend suggested we get bark collars. I purchased the Awaiymi Bark Collar 2 Pack Upgraded 7 Sensitivity Rechargeable Dog Barking Collars preparing to be disappointed. The first walk was tough. Vibration alone was not effective. Halfway through, we switched to the second lowest shock setting. The dogs got shocked quite a few times on the way home and we felt bad. The second day was better. The terrier cowered quite a bit when we put on the collars. On the walk, they each got one shock from barking before they both figured out somehow that they could whine but not bark at other dogs to avoid a shock. The third day was better still. We had no barking, no whining, no shocking. We praised them every time they calmly passed another dog. On the fourth and fifth days, they totally ignored other dogs and we gave them a treat every time they passed a dog with no incident. On the sixth day we turned the shock off and walked with no incident-praising every good encounter. We are frankly amazed. Hope you have the same results.