ULTRASONIC FUNCTION - Based on the theory that the dog trainer can effectively train your dogs to be obedient and discourage unwanted behaviors like barking, digging, chewing and more. Besides, they are harmless to both humans and pets. EASY TO USE - Open the battery cover first, then insert a 9V battery (not included). The sound is only audible for pets. Finally, turn on the switch and it can work well. It can also be used as a flashlight if needed. LED FLASHLIGHT BATTERY INDICATOR - Super bright LED flashlight function is helpful when walking or jogging at night, which also doubles as a battery indicator. HAND-FRIENDLY CONVENIENCE - This device can be used anywhere - The device is about 12.5 * 4 * 2.7cm / 5 * 1.6 * 1.06in in size, portable and handy, also convenient to take with you, e.g. such as jogging or hiking, cycling, parking, etc. MULTI-FUNCTION - Except as a pet exercise tool, it can also protect you from dog attacks. It is suitable for training many types of dogs, e.g. B.