Abstract: A radiation detector includes a new and sensitive radiation sensor. The sensor includes a photo conductor cell. A substantially transparent cone optically coupled to the photo conductor cell, and a first layer of phosphor material coated onto the transparent cone. The layer of metal is then coated onto the phosphor material. This combination provides a sensitive and compact sensor construction. A bias light is further included to improve the sensitivity of the sensor. Signals sent by the sensor and evaluated by a microprocessor result in the transmission of predetermined audible sounds.