A method for detecting decalibration of a device for analyzing particles, including irradiating particles with light, detecting light scattered from the particles, amplifying, digitizing and detecting the electric signal obtained in a plurality of digital channels corresponding to the intensity representing the particle size and monitoring the appearance of the Mie peak in the measured size-dependent frequency distribution and sending a report if the Mie peak deviates in a digital channel other than the digital standard channel belonging to it based on measurement settings. The electronic analyzing unit detecting a Mie peak in the measured particle size distribution and assigning it to a digital detection channel in a device for detecting the concentration of small particles in gas, with a sample tube, a light source, a detector detecting scattered light scattered on the particles, an analog amplifier, an analog-digital converter, an electronic analyzing unit and a display and operating unit.