Background: Despite the importance of prompt epinephrine auto-injector (EAI) treatment during anaphylaxis, proper administration technique is often lacking among patients and caregivers. Objective: To compare usability and participant preference of Auvi-Q and EpiPen Jr EAIs in a simulated lifethreatening allergic emergency-use scenario. Methods: In this randomized, crossover, human-factors usability study, untrained adults (18-65 years) were tasked with using 0.15 mg Auvi-Q and EpiPen Jr trainers to simulate epinephrine administration to a childsized manikin. Only written instructions on the device label and/or device voice instructions were available to participants. Endpoints included completing injection tasks per device instructions (primary endpoint), completing key injection tasks, and participant preference/ratings of devices. Completion of injection tasks were evaluated using a McNemar test for paired dichotomous data. Results: Ninety-six adults were included in study analyses. Significantly more participants completed all injection tasks per device instructions with Auvi-Q (85.4%) vs EpiPen Jr (19.8%; P < .001). Significant differences were also observed for completion of key injection tasks (Auvi -Q, 94.8%; EpiPen Jr, 72.9%; P < .001). No digital/hand injection errors were seen with Auvi-Q, whereas 14 participants (14.6%) would have accidentally received a digital/hand injection with EpiPen Jr (P < .001). Overall, significantly more participants preferred Auvi-Q over EpiPen Jr (91.7% vs 6.3%; P < .001 [2.1% no preference]). Median scores for 8 EAI characteristics were also higher for Auvi-Q vs EpiPen Jr. Conclusion: In this study, untrained adults preferred and were more likely to use Auvi-Q correctly vs EpiPen Jr, highlighting the importance of device design for successful epinephrine administration during a lifethreatening allergic emergency.