The rapid development of technology based on mobile devices in recent years impacts late adolescents. Therefore, this study aims to determine the intensity of mobile device checking as one important indicator of FOMO behavior in late adolescents. A quantitative study using a survey method was chosen as the method in this study, with 98 late adolescents selected as respondents. There were several alternative answer choices provided which were then selected by the respondents to describe the intensity of mobile device checking in late adolescents, where the options were checking the devices every minute, every hour, every few hours, and others/filling in themselves. The results showed that 76% of late adolescent at least checked their devices tens or even hundreds of times a day. This data can be one indicator that most late adolescents are indicated by the FOMO phenomenon due to the tendency of maladaptive mobile device checking behavior.