The BC-200 is smaller than all other No-Bark systems. It is the most advanced and effective bark control collar on the market today. Because it is lightweight, it is ideally suited for smaller dogs. The rugged waterproof collar makes it the choice for the all-weather outdoor dog. It is also popular for those who do not want to change batteries, but instead want a rechargeable system. After charging, the collar will work for 30 - 72 hours, depending on the need for correction. Because of advanced technology, there are no external vibration sensors; all the electronics are housed within the rugged case. This No-Bark system electronically and specifically detects the bark of the dog wearing the collar, not just any dog or any bark, so your dog will not receive a correction unless your dog does the barking. This makes it safe to use when you have more than one dog. Plus, if you have two or more barkers, each can wear his own collar and will only receive a correction when he does the barking.