Aims: To test the performance of the cardiac vagal tone (CVT) derived from a 5-minute ECG recording compared with the standardized cardiovascular autonomic reflex tests (CARTs). Methods: Cross-sectional study included 56 well-phenotyped adults with type 1 diabetes (19–71 years, 2–54 years disease-duration). Autonomic testing included: standardized CARTs obtained with the VAGUS™, CVT, and indices of heart rate variability (HRV) obtained at 24- and 120-hour, and electrochemical skin conductance assessed with SUDOSCAN®. ROC AUC and cut-off values were calculated for CVT to recognize CAN based on ≥ 2 (established CAN, n = 7) or 1 (borderline CAN, n = 9) abnormal CARTs and compared to HRV indices and electrochemical skin conductance. Results: Established CAN: The cut-off CVT value of 3.2LVS showed 67% sensitivity and 87% specificity (p = 0.01). Indices of HRV at either 24-hour (AUC > 0.90) and 120-hour (AUC > 0.88) performed better than CVT. Borderline CAN: The cut-off CVT value of 5.2LVS indicated 88% sensitivity and 63% specificity (p = 0.07). CVT performed better than HRV indices (AUC < 0.72). Electrochemical skin conductance (AUC:0.63–0.72) had lower sensitivity and specificity compared with CVT. Conclusions: Implementation of CVT with a clinically applicable cut-off value may be considered a quicker and accessible screening tool which could ultimately decrease the number of unrecognized CAN and initiate earlier prevention initiatives.