Kiryat Shema (saying the Shema) is more than saying a few lines casually.  There is halacha surrounding the proper recitation. 

In Kiryat Shema, the first line of declaration is said aloud.  The second line, "Baruch Shem Kavod Malchuto L'olam Vaed" is to be said in an undertone, almost a whisper (Pesachim 56a).  The only day of the year in which the second line is to be said aloud is on Yom Kippur.  It is on this day that we are clad in white, holy like the angels, and able to declare this statement with a full voice.  In declaring both lines, whether aloud or in a whisper, they are to be said with clear articulation and kavannah (intention).

Also, when saying the Shema not in the presence of a minyan, the extra "El Melech Ne'eman" (which means "G-d, Faithful King") is said before Kiryat Shema.When praying without a Minyan, these three words are added, to make up 248 words, since there is no Chazzan to repeat the last three words of the Shema. This number corresponds to both the number of the positive Mitzvos and the number of the organs in our body.