Driving while intoxicated (DWI) results in significant morbidity and mortality. Ignition interlock devices (IID) decrease the risk of drinking and driving while installed, but DWI rates increase after the IID is removed. Efforts are needed to maintain change after the IID is removed; engaging concerned family members (CFMs) is an untested strategy. Smartphones may provide a promising platform to support DWI offenders with IIDs and their CFMs; the purpose of the present study was to develop such a smartphone-web app. Formative work occurred in two sequential phases. Phase 1 included key informant interviews with DWI offenders and CFMs, development of one app module, and usability testing. Phase 2 included focus groups with DWI offenders and CFMs, development of three more app modules, and usability testing. The Bangor System Usability Scale was used to rate app usability and navigability. Results of key informants and focus groups indicated that offenders and CFMs lacked information and were frustrated by the IID, experienced financial burden from the DWI and IID, viewed supportive communication and positive shared activities as important, and were positive about the app. Four modules were developed, Life with Interlock, Supporting Changes in Drinking, Doing Things Together, and Effective Communication. Usability testing indicated that the B-SMART modules were easy to use and informative. Careful formative work resulted in an app responsive to the concerns of DWI offenders with IIDs and their CFMs. Controlled research is needed to evaluate the efficacy of the app.