We're plagued by unwanted cats coming into our garden, particularly at night so I ordered two of these and am very pleased to say that they work. There are also settings to repel other pests including rats, dogs and foxes.
However, although the design has changed slightly from the illustration, a battery change involves removing all of the screws and taking the unit apart. The screws are deeply recessed in the back of the unit and thanks to this silly design, water also collects in the recess with the result that the screws soon rust. It is then very difficult to remove them without damaging their heads. This really should be reviewed by the manufacturer but, in the meantime, I strongly advise applying a layer of Vaseline to the screw heads (and the threads too - anything which helps with their removal has to be beneficial) and applying a layer of waterproof tape over the holes.
All in all, it's a lot of bother considering the batteries will need to be changed every month. It's a shame - because the unit does actually work better than others available.