The US EPA has identified 15 radon measurement methods in air. Each of them has advantages and disadvantages, requires different types of devices to detect a radiation. The purpose of this work is improvement of AC method - activated charcoal adsorption method. The detector consists of electronic unit (200x180x80 mm) and scintillation cell (a tube with diameter of 60 mm and length 200 mm). The electronic unit contains power supply, amplifier, discriminator, timer, counter and indicator. The scintillation cell contains the zinc sulfide scintillator, photomultiplier, preamplifier, high voltage power supply and chamber with volume of 200 mL over the scintillator. This chamber is intended to situate activated carbon fibrous absorber and air compressor. For this method, air is drawn through a filter to remove radon decay products and then through the activated carbon cloth by using the compressor. Sampling takes from 5 to 15 minutes. After sampling the cloth is heated during 5-10 sec by electric current passing through the fiber up to 200-250oC. Radon gas evaporates from the cloth and the device detects scintillation counts. Due to high coefficient of radon concentrating (adsorption of radon by the activated carbon cloth from large volume of air of 50-150 l and evaporating into small volume of the chamber) the method has detecting limit of 2-4 Bq/m3. As the distance between the filter, cloth and scintillator is more than 80 mm, the detector measures only radiation of radon and not from radon decay products remained in the filter and cloth.