"Know Addiction", as the name suggests, helps mobile phone users to "know" (Addiction) their own use of the phone (Addiction), and "prevent" excessive addiction (No Addiction). This is the world's first actuarial time app. We found that "Apps record mobile phone time by 50% more than consciously." For example, college students who think they use their mobile phones for about 20 hours per week, install the app we developed and found that their actual use time is 50% longer than they realized, reaching 30 hours. And the longer the phone is used, the greater the degree of underestimation of actual use.