Abstract: Local radiation exposure alarm having a radiation detector used in the course of operations in nuclear power plant, a radiotherapeutic center for treatment for cancer, etc., a preamplifier for transmitting with an excellent S/N ratio a detected output signal from said detector, and a measuring unit measuring an exposure and provided with an alarm operating when the exposure exceeds a set permissible dose, and in which these detector, preamplifier and measuring unit are connected together electrically. The detector unit is shaped in a ring to be set on a finger or a toe, has a semiconductor element highly sensitive to radiation such as gamma rays incorporated therein so as to be sufficiently protected from vibrations and moisture, and is connected to the preamplifier unit through a lead wire.