Sound stimuli is one of the easiest kinds of stimuli to catch people's attention. For example, visual stimuli requires the person to already be focusing on a area close to the stimuli. Imagine you are sitting in a classroom texting on your phone. Chances are, you are not going to notice someone waving to you across the room. However, if someone were to start screaming at a high volume, you are going to notice a lot more quickly. This is partly due to the fact that sound stimuli sends vibrations to your body, alerting you more quickly. This is why smoke detectors, sirens, car horns and other sound stimuli work so well at catching your attention.