Abstract The comfort of indoor occupants is the primary factor infl uencing the energy consumption in a building. Even if it is a highly subjective notion, a better understanding of its links with the environmental parameters represents a promising way to optimize building energy consumption. The environmental physical parameters can be easily measured but usually require multiple and/or expensive systems. In this work, we present the conception and the calibration of an inexpensive and straightforward homemade diagnostic tool named VisAcTh, dedicated to measuring the environmental parameters related to indoor thermal, visual, and acoustic comforts. We paid particular attention to the simplicity of the diff erent methods and concepts used in the conception, operation, and calibration. The VisAcTh tool comprises six inexpensive sensors controlled by an ESP32 microcontroller integrated into a 3D-printed PLA box. It allows measuring air temperature, air velocity, mean radiant temperature, relative humidity, atmospheric pressure, noise level, and illuminance. Three sensors require a calibration step to operate in specifi c indoor conditions, i.e., the homemade globe thermometer, the noise level, and the air velocity sensors. We designed protocols based on a homemade experimental setup that can be easily built using machines available in most fablabs and by scientists with limited knowledge. The last part of the paper is dedicated to evaluating the reliability and performance of the device. Two sets of experiments are performed, during which we monitor the noise level, the illuminance, and the well-known predicted mean vote, which depends on thermal physical parameters. The fi rst one aims to evaluate the reliability of the VisAcTh device by comparing it with reference sensors over a period of a few hours in three spaces of an education building (a classroom, a lobby, and an offi ce). A good agreement was found between these measurements and similar ones obtained from commercial and calibrated sensors. Second, we aim to evaluate the monitoring capability of the device during an extended period. Thus, four new VisAcTh are built, calibrated, and placed in four rooms of a modular education building for four months. The results are in line with the environmental conditions.