The present invention relates to a cartridge-in-chamber detection system for weapons wherein the state of the cartridge in the chamber is independent in order to provide a reliable indication of the presence or absence of the cartridge in the chamber of the weapon, wherein the system comprises means to, through a supply voltage, determine the variation of the electrical capacity between the two possible states of the system, when there is no cartridge in the chamber and when there is a cartridge in the chamber, making use of at least one electrode, without the cartridge intervening in the system.