Excelvan Rechargeable and Waterproof 100 level vibration and shock training system with lcd display--for 2 dogs Package Including: 1 X remote control unit; 2 X collars; 1 X charger & cord; 2 X test light & replacement probes; 1 X Operating Instructions. 100 levels of vibration. 100 levels of static. The levels can be altered by use of up & down button. The system can be used for 2 receivers. The life span of the batteries vary to how often you use the product. Therefore you should often check the batteries by hearing the beep from the Collar Receiver and watching the indicator light on the LCD screen of the Transmitter. The valid distance of remote control means the straight-line distance between the Transmitter and the Collar Receiver without obstacles in between. If there are interference source around, the actual remote control distance may vary. This product is for pet training only by training, the pet can understand the intention of its owner. Desirable results can only be achieved after a period of training. Training sessions should be kept positive and short, about 10-15 minutes each time.