Nowadays, it is very important to detect dangerous gases and alert the emergency services in time; furthermore, given that detectors presently available in the market achieve a high price, the goal was to make a cheap and accurate device that is available to everyone. Within the works covered in this paper, a device of the kind was designed and constructed with the aim of monitoring the concentration of CO and flammable gases. The gas concentration monitoring device uses widely available technology that makes a unique connection with a sensor as an input, a microcontroller as a control unit and an LCD display output. The device is easy to make and it is cheaper than other devices currently present in the market. The device is built into a plastic housing and monitors the gas concentration in real time. After the assembling of the hardware components and placing them into the plastic housing, the software was implemented thus programming the microcontroller to control the complete system. Based on the study and implementation of the gas detector project, it was concluded that the device has a high sensitivity to hazardous gas concentrations and that it is of a great benefit because it would allow easy control of air quality in households. To demonstrate the feasibility and efficiency of the system, this paper presents the results of a system for monitoring the concentration of CO gases and flammable gases indoors where there are gas water heaters used by households for heating and hot water. The advantage of the device is that it primarily reduces not only the number of victims of poisoning with hazardous gases but it as well reduces fire hazards in general.