Post Bariatric Closed Loop Glucagon Trial

Inclusion Criteria: * Age 21 years or older with a gastric bypass for more than 1 year. * Post-bariatric hypoglycemia with prior episodes of neuroglycopenia, unresponsive to dietary intervention (low glycemic index, controlled carbohydrate portions) and trial of acarbose therapy at the maximally tolerated dose. Other therapies will not exclude a subject as long as the therapy is continued during the study. * Otherwise healthy (mild chronic disease such as asthma, hypertension, and depression will be allowed if well controlled). * Self-reported frequency of documented hypoglycemia (BG \< 60 mg/dl verified by capillary blood glucose measurements) of at least 2 times per week. Exclusion Criteria: * Unable to provide informed consent. * Unable to comply with study procedures. * Current participation in another hypoglycemia related clinical trial other than one that is primarily observational in nature. * Pregnancy (positive urine HCG), breast feeding, plan to become pregnant in the immediate future, or sexually active without use of contraception. * Use of insulin and/or insulin secretogues as sulfonylurea, metglitides, and glitazones. * History of cystic fibrosis, pancreatitis, type 1 diabetes or other pancreatic disease. * End stage renal disease on dialysis (hemodialysis or peritoneal dialysis). * Any known liver or biliary disease including cirrhosis, alcoholic liver disease, non-alcoholic fatty liver disease, non-alcoholic steatohepatitis, any form of viral hepatitis. * Congestive heart failure (established history of CHF, paroxysmal nocturnal dyspnea, or orthopnea). * Acute illness or exacerbation of chronic illness at the time of the study. * Known insulinoma or predominantly fasting pattern of hypoglycemia * Adrenal insufficiency. Congenital hyperinsulinemia presenting with hypoglycemia during infancy. * History of pheochromocytoma. Fractionated metanephrines will be tested in patients with history increasing the risk for a catecholamine secreting tumor: * Paroxysms of tachycardia, pallor, or headache. * Personal or family history of MEN 2A, MEN 2B, neurofibromatosis, or von Hippel-Lindau disease. * Episodic or treatment refractory (requiring 4 or more medications to achieve normotension) hypertension. * Untreated or inadequately treated mental illness (indicators would include symptoms such as psychosis, hallucinations, mania, and/or any psychiatric hospitalization in the last year). * Current alcohol abuse (intake averaging \> 3 drinks daily in last 30 days) or substance abuse (any use within the last 6 months of controlled substances without a prescription). * Unwilling or unable to refrain from drinking more than two drinks in an hour or more than four drinks in a day during the trial. * Electrically powered implants (e.g. cochlear implants, neurostimulators) that might be susceptible to RF interference. * History of adverse reaction to glucagon (including allergy) besides nausea and vomiting. * Unwilling or unable to completely avoid acetaminophen during the study period. * Any factors that, in the opinion of the principal investigator, would interfere with the safe completion of the study procedures.