A method performed by an apparatus included in a vehicle to detect an object using a radar includes: propagating, in a normal mode period of an operating period for detecting objects, a normal mode transmission signal generated based on a default code sequence including at least two codes; receiving a normal mode reception signal in the normal mode period; detecting, in the normal mode period, an object based on the default code sequence and the normal mode reception signal; receiving a listening mode reception signal in a listening mode period of the operating period; acquiring a correlation between the listening mode reception signal and the default code sequence; and changing the default code sequence based on the correlation.