An electronic apex locator is an electronic device used in endodontics determine the position of the apical constriction and thus determine the length of the root canal space.The apex of the root has a specific resistance to electrical current, and this is measured using a pair of electrodes typically hooked into the lip and attached to an endodontic file.Today’s Dental apex Locators are small, light-weight and portable, with displays showing the approximate distance from the file tip to the apex and indicating when the apical foramen is reached. Many devices have audible alarms.Electronic apex locators detect the transition of pulp to periodontal tissue with accuracy to within .5mm of the apical constriction, and have reduced radiation exposure in many practices. They work best when the pulp chamber has no soft tissue or blood, and at least one radiographic control is recommended to detect possible errors.