Device (3) for providing a warning signal when the fan cowl doors (8, 9) of an aircraft are not properly latched by primary locks (6), wherein the device comprises a panel (4) the panel (4) being rotatably mounted on one of the two fan cowl doors (8 or 9), the panel (4) being closed on that one fan cowl doors (8 or 9) by rotation thereby covering at least partially the primary locks (6), such that all the primary locks (6) have to be properly latched for the panel (4) to be closed, and at least one of the panel (4) primary locks (6) not being properly latched prevents proper closing of the panel (4).