Just thought it might be a good idea to let everyone know. Two years ago, I downloaded one of these apps in hopes of silencing an annoying loud and scary herd of vicious dogs in a yard I was passing by. The high pitched tone produced by the app not only annoyed the living daylights out of me, but also caused the vicious dog herd to go completely insane and become quite a hazard (more than quadrupled barking intensity, loud enraged growling, almost jumping over decently tall fence in hopes of attacking me... ). Whatever you do, do not impulsively download/use one of these apps if you know what's good for you . I'm pretty sure there are better ways to deal with bothersome vicious attack dogs.