Think of the sound as a cue for your dog to do a behavior (such as touch your leg). So play the sound, wait 2 seconds, cue the dog to touch. Repeat 50times and your dog will start to anticipate that sound=touch. Just make sure you're not making eye contact with the dog, moving your leg, or giving off other body language that will overshadow the sound and hinder your dog doing the alert in real life.