Abstract: A device and method for preventing transfusion of incompatible blood comprises a means for performing the following procedures. Upon admission to the hospital, a rapid blood type test is performed in the presence of the patient and, immediately thereafter, a wrist band with a key or other releasing means corresponding to the patient's blood type is secured to the patient's wrist. A locking mechanism is provided on all blood bags in the blood bank at the time of the blood donation which corresponds to the blood type contained in the bag and is color coded. Blood is dispatched from the blood bank for a patient upon request after the usual crossmatching. Upon arrival at the patient's location, the bag is unlocked using the key attached to the patient's wrist band and the blood transfusion is administered.