Most car accidents are caused by improper driving behaviors. Studies have shown that changing lanes improperly is one of the main causes of traffic accidents. This shows that drivers need an assisting alarm system to help them avoid the danger during overtaking. We also found that the existing alarm system and researches try to use different sensory outputs as the alarm signals. However, there were no studies to compare how the different sensory alarm signals affect the drivers. Therefore, in this study, we have setup three kinds of alarm signals (visual, sound, and haptic alarm signals) to see which one is more suitable at the high speed context. On top of that, the sensitivity of the alarm system may be the other key factor that affects drivers' behaviors. So, we manipulate two most commonly shown alarm signal frequencies when the driver feels threatened. The results of this study have proven that the sound and haptic signals are better than visual outputs when drivers are put in a high visual loading situation. This result could be the guideline for future designers of a driving alarm system.