While responding on a lifeline medical call we gained entry to the residence via the keys in the possession of our department. The house was dark and quiet. We called loudly to the known occupant of the home, receiving no answer, we proceeded to check the house for the patient. As we started to climb the stairs to the 2nd floor we heard the unmistakable sound of a round being jacked into a shotgun. We yelled loudly at the occupant while scrambling down the stairs and around the corner of the hallway. After a short discussion the occupant, an 80 year old male, realized who we were and put the gun away. The occupant had rolled over on his lifeline activator and had no idea we were coming, just thought he was protecting his home from intruders