This collar is exceptional and it comes with two for the price of one, I was surprised and didn't expect that. You can keep one device charged at all times and just swap out unit when it starts beeping warning you the rechargeable battery is low of use both units for two dogs. I love that its waterproof! It's well designed and sturdy construction with a LCD display and 99 levels of static, 99 levels of vibration and a beep mode. I've used the vibration before the static tingle and it only took two times before the vibration is now all I need to stop her from barking (they learn fast) I tried the static on myself and it's a lite tingle which does not hurt the dog. One charge of the battery lasts two or three days when you first start training your dog and after that with not using it so much it lasts much longer on one charge. I recommend this product highly and it's well worth the price to include two units.