OBJECTIVE To assess the efficacy of the insulin pen cap Insulclock on improving glycemic control, treatment adherence, and user satisfaction in people with type 1 diabetes. RESEARCH DESIGN AND METHODS This multicenter, open-label, randomized controlled trial comprised a 4-week run-in phase and a 6-week double-arm phase in which participants were randomly assigned into an active or masked mode. RESULTS Fifty-five participants were evaluable (active group, n = 26, masked group, n = 29). The increase in time in range was higher in the active versus masked group (5.2% vs. −0.8%; P = 0.016). The active group showed a higher reduction in mean glucose, glucose management indicator, time above range, and high blood glucose index. On-time insulin doses increased in the active group and decreased in the masked group. CONCLUSIONS Insulclock system use was associated with improved glycemic control, glycemic variability, hyperglycemia risk, and treatment adherence in people with uncontrolled type 1 diabetes.