<p dir="ltr">Behavior-change theories reliably explain behavior, but they often lack messaging recommendations to modify behavior. The Theory of Planned Behavior (TPB) could benefit from clear, replicable messaging strategies to target its constructs of attitudes, social norms, and perceived behavioral control (PBC) about a behavior (Ajzen, 1991). Habit Theory is commonly used for behavior-change interventions because it offers both behavior-change explanations and messaging (Orbell & Verplanken, 2020). Its habit strength measure has been used repeatedly to add explanatory power to the TPB model, and this study tests whether its messaging strategies can effectively pair with the TPB to affect PBC and instigate behavior change (Bamberg et al., 2003; Bayer & Campbell, 2012).</p><p dir="ltr">To test these strategies in the context of problematic smartphone use among college students, focus groups were conducted to select a target habit and to refine the messaging strategy and channel for a habit-focused intervention. These findings were used to create and conduct an intervention with a sorority at Purdue University, and a pre-test, post-test, delayed post-test survey design was used to analyze the effectiveness of the intervention. The intervention had positive effects on participants’ attitudes and intentions toward implementing the habit and to reduce smartphone use, improved their habit strength, and increased the number of times they put their smartphones out of sight while studying or doing homework. Additionally, the sticker cues given away during the intervention increased the effects of the intervention for those who affixed them to at least one of their devices. However, the intervention did not affect PBC or time spent on a smartphone. These findings emphasize the importance of continued research into how messaging strategies affect behavior and the constructs within the TPB.</p>