The core instrument of the Space-based multi-band Variable Objects Monitor gamma-ray burst mission launched in 2024 June is the 4–150 keV 2D coded mask camera ECLAIRs responsible for the autonomous trigger and localization of transient events within its field of view. The flight model of ECLAIRs has been built by several French labs (IRAP, CEA, APC) under the supervision of the French Space Agency (CNES), while APC, LUPM and IAP built a suite of data reduction and analysis software. This paper outlines the main science goals of ECLAIRs and describes the different instrument subsystems and their main characteristics. The paper then discusses the instrument configuration and operation as well as the main in-flight measured performances. Finally the paper summarizes the science performance of ECLAIRs up to 2025 March 31.