The ability to deter rule violations is based on the certainty, celerity, and severity of punishment for noncompliance; however, a disproportionate share of public policies and program evaluations focus on severity. In this paper, we evaluate a large-scale effort to significantly increase certainty and celerity of sanction for an offense while keeping severity low: South Dakota's 24/7 Sobriety Program (hereinafter, 24/7). 24/7 is a criminal justice intervention requiring those arrested for or convicted of an alcohol-related offense (e.g., driving under the influence, domestic violence) to abstain from alcohol and be tested for alcohol multiple times per day. Those testing positive for alcohol or missing a test are subject to a swift, certain, and moderate sanction, typically a night or two in jail. From 2005 through February 2017, more than 30,000 unique South Dakotans participated in 24/7. To estimate the causal effect of 24/7 on the probability of being arrested or having probation revoked, we use program availability in a county as an instrument for individual participation. The results show that 24/7 participation had a large effect on criminal behavior: We estimate that the probability a 24/7 participant was rearrested or had probation revoked 12 months after being arrested for driving under the influence was 49 percent lower than that of non-participants (p = 0.002). We also detected reductions at 24 and 36 months—35 percent (p = 0.013) and 26 percent (p = 0.009), respectively. These results provide evidence that it is possible to create a credible and effective deterrent threat on a large scale by prioritizing both certainty and celerity of sanction.