<p>Smartphones enable both easy reservations of motel accommodations and carefree searches for sexual partners. This study investigates the relationship between smartphone use, motel spending, and the prevalence of sexually transmitted infections in South Korea. Monthly data (N = 72) from December 2017 to November 2023 were analyzed, combining information on diagnosed sexually transmitted infection cases from the Korea Disease Control and Prevention Agency, smartphone users from the Korean Statistical Information Service, and motel credit and debit card spending from the Korea Tour Data Lab. Using a vector error correction model from time series analysis, the results show that smartphone use Granger causes both higher motel spending and higher incidences of sexually transmitted infections. The latter effect is particularly pronounced in cases of condyloma, suggesting that smartphone use may disproportionately impact the gay community, as condylomas are more common among men who have sex with men. In addition to the effect of smartphone use, motel spending is found to Granger cause a higher incidence of sexually transmitted infections. The evidence thus indicates a direct and indirect influence of smartphone use on the spread of sexually transmitted infections. These findings highlight the complex relationship between technology adoption, behavioral patterns, and public health concerns, and underscore the need for targeted interventions and awareness campaigns to mitigate potential adverse effects associated with smartphone-driven behavior.</p>