If you want to make sure that a zapper works properly, you should turn it on and listen if it makes a sound. That will indicate the electricity flow. Then you can turn it off and listen if the sound disappears. You may also check if the light is right, but you need the protective goggles. But when you choose online, you can’t do this. So, I recommend you to choose from the top 5 products I have described – they work properly.