I bought the repellent for cats and after 1 month of using it, I can tell you the following. It has 2 options, one that says it is for training and the machine is silent and it repels cats from a distance of 3-4 meters, but you have to aim at them. The second option produces a louder sound but it is more effective and generally repels cats from the area without needing to aim at them. In order for the machine to work effectively, it needs a battery, and as the battery runs out, its effectiveness decreases. The battery it comes with is better not to be used at all because it is very weak to the point where I initially thought the machine was not working. I give it 4 stars because in its most effective mode, the noise it makes is audible, and it quickly drains the batteries (I used 3 batteries in one month), so I had to buy a rechargeable battery (I bought a 9V with micro USB for around €11).