The open-loop system will be set to recognize low sensor glucose values, triggering an alert to the physician, who will deliver a bolus of 150 or 300 µg of glucagon via the pump, with the goal of preventing further decline in glucose values. Depending on response, a second bolus dose of 150 or 300 µg of glucagon may be administered. Plasma glucose will be measured after glucagon administration to ensure successful treatment and glucose stability, and glucagon levels will be analyzed concurrently to determine magnitude of increase above baseline. Sensors will be downloaded for subsequent analysis of appropriateness of alert timing and trigger for glucagon bolus delivery.