The relay method for an alarm system of the present invention includes: a third process in which a reception intensity of the acknowledgement signal is measured when the source alarm device receives the acknowledgement signal, and in which, if there are one or more destination alarm devices that have not transmitted the acknowledgement signal among all of the destination alarm devices registered in advance, a destination alarm device that has the lowest reception intensity of the acknowledgement signal is assigned as a relay destination alarm device; and a fourth process in which an abnormality signal is relay-transmitted from the source alarm device, through the relay destination alarm device, to the destination alarm devices that are interconnected with the relay destination alarm device, and then, from the destination alarm device that has received the abnormality signal, a signal indicating that a sender thereof is the destination alarm device is outputted, and also an acknowledgement signal is transmitted to the source alarm device. In addition, when there are one or more all of the destination alarm devices which have not transmitted an acknowledgement signal to the source alarm device among all of the destination the alarm devices registered in advance, the third and fourth processes are repeated.