There are several ways of measuring absorbed doses from ionizing radiation. People in occupational contact with radioactive substances, or who may be exposed to radiation, routinely carry personal dosimeters. These are specifically designed to record and indicate the dose received. Traditionally, these were lockets fastened to the external clothing of the monitored person, which contained photographic film known as film badge dosimeters. These have been largely replaced with other devices such as Thermoluminescent dosimetry (TLD), optically stimulated luminescence (OSL), or Fluorescent Nuclear Tract Detector (FNTD) badges.