Siman 75
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א טֶפַח מְגֻלֶּה בְּאִשָּׁה בְּמָקוֹם שֶׁדַּרְכָּהּ לְכַסוֹתוֹ, אֲפִלּוּ הִיא אִשְׁתּוֹ, אָסוּר לִקְרוֹת קְרִיאַת שְׁמַע כְּנֶגְדָּהּ: הַגָּה: וְיֵשׁ אוֹמְרִים דַּוְקָא בְּאִשְׁתּוֹ, אֲבָל בְּאִשָּׁה אַחֶרֶת אֲפִלּוּ פָּחוֹת מִטֶּפַח הֲוָה עֶרְוָה (הַגָּהוֹת מַיְמוֹנִי פֶּרֶק ג') וְנִרְאֶה מִדִּבְרֵי הָרֹא"שׁ דְּטֶפַח בְּאִשָּׁה עֶרְוָה אֲפִלּוּ לְאִשָּׁה אַחֶרֶת, רַק שֶׁבְּעַצְמָהּ יְכוֹלָה לִקְרוֹת, אַף עַל פִּי שֶׁהִיא עֲרֻמָּה כְּדִלְעֵיל סי' ע"ד.
1 To Be Careful of Exposed Hair and the Voice of a Woman at the Time of the Recitation of the Sh'ma and So Not to Recite It in Front of the Nakedness - Containing 6 S'ifim If a handbreadth is uncovered on a woman in a place [on her body] where the practice (lit. way) is to cover it, even if it his wife, then it is forbidden to recite the Recitation of the Sh'ma in front of her. Rema: And there are those who say that this is specifically with respect to his wife, but with another woman even less than a handbreadth is [considered] nakedness (Hagahot Maimoni Chapter 3). And it seems from the words of the Rosh that a handbreadth on a woman is [considered] nakedness even [in regards] to another woman, except that to herself she is able to recite [the Recitation of the Sh'ma] even though she is naked like was said earlier in Siman 74.
ב שֵׂעָר שֶׁל אִשָּׁה שֶׁדַּרְכָּהּ לְכַסוֹת, אָסוּר לִקְרוֹת כְּנֶגְדּוֹ: הַגָּה: אֲפִלּוּ אִשְׁתּוֹ אֲבָל בְּתוּלוֹת שֶׁדַּרְכָּן לֵילֵךְ פְּרוּעוֹת הָרֹאשׁ, מֻתָּר: הַגָּה: וְה"ה הַשְּׂעָרוֹת שֶׁל נָשִׁים שֶׁרְגִילִין לָצֵאת מִחוּץ לְצַמָּתָן (בֵּית יוֹסֵף בְּשֵׁם הָרַשְׁבָּ"א) וְכָל שֶׁכֵּן שְׂעַר נָכְרִית, אֲפִלּוּ דַּרְכָּהּ לְכַסּוֹת (הַגָּהוֹת אַלְפָסִי הַחֲדָשִׁים):
2 The hair of a woman that it is the practice (lit. way) to cover is forbidden to recite [the Recitation of the Sh'ma] in front of it. Rema: Even his wife. But unmarried women for whom it is their way to go with an uncovered head, it is permitted. Rema: And so too is the law with the hairs of women that regularly come out of their covering (Beit Yosef in the name of Rashba) and certainly foreign hair (i.e. a wig) even if it is her practice to cover (Hagahot Alfasi haChadashim).
ג יֵשׁ לִזָּהֵר מִשְּׁמִיעַת קוֹל זֶמֶר אִשָּׁה בִּשְׁעַת קְרִיאַת שְׁמַע הַגָּה: וַאֲפִלּוּ בְּאִשְׁתּוֹ, אֲבָל קוֹל הָרָגִיל בּוֹ אֵינוֹ עֶרְוָה (בֵּית יוֹסֵף בְּשֵׁם אֹהֶל מוֹעֵד וְהַג"מ).
3 One should be careful from hearing a woman's singing voice at the time of the Recitation of the Sh'ma. Rema: And even with his wife. But a voice that one is familiar with is not [considered] nakedness. (Beit Yosef in the name of Ohel Moed and Hagahot Maimoni)
ד אָסוּר לִקְרוֹת כְּנֶגֶד עֶרְוָה אֲפִלּוּ שֶׁל עַכּוּ"ם, וְכֵן כְּנֶגֶד עֶרְוַת קָטָן אָסוּר: וְיֵשׁ מַתִּירִין נֶגֶד עֶרְוַת קָטָן, כָּל זְמַן שֶׁאֵינוֹ רָאוּי לְבִיאָה (רַבֵּנוּ יְרוּחָם הָרֹא"שׁ פֶּרֶק מִי שֶׁמֵּתוֹ וּמהר"א מִפְּרַאג) וְכֵן עִקָּר וְעַיֵּן בְּיוֹרֵה דֵּעָה סִימָן רס"ה.
4 It is forbidden to recite [the Recitation of the Sh'ma] in front of "nakedness", even that of a non-Jew and so too in front of the "nakedness" of a minor it is forbidden. And there are those that permit [it] in front of the "nakedness" of a minor so long as [the child] is not considered capable of sexual intercourse (Rabeinu Yerucham - the Rosh on Chapter "Mi Shemeito" and Mahara of Prague). And that is the main opinion. (see Yoreh Deah, Siman 265)
ה עֶרְוָה בַּעֲשָׁשִׁית וְרוֹאֶה אוֹתָהּ דֶּרֶךְ דָּפְנוֹתֶיהָ, אָסוּר לִקְרוֹת כְּנֶגְדָּהּ, דִּכְתִּיב וְלֹא יִרְאֶה בְךָ עֶרְוַת דָּבָר, וְהָא מִתְחַזְּיָא.
5 If there is "nakedness" behind a [glass] lamp and one sees it through the [glass] walls [of the lamp], it is forbidden to recite [Sh'ma] in front of it, as is written, "...let Him not find anything unseemly among you" (Deut. 23:15) and here, it is seen.
ו הָיְתָה עֶרְוָה כְּנֶגְדּוֹ וְהֶחֱזִיר פָּנָיו מִמֶּנָּה, אוֹ שֶׁעָצַם עֵינָיו, אוֹ שֶׁהוּא בַּלַּיְלָה, אוֹ שֶׁהוּא סוּמָא, מֻתָּר לִקְרוֹת, דְּבִרְאִיָּה תָּלָה רַחֲמָנָא, וְהָא לָא חָזֵי לָהּ:
6 If there was "nakedness" if front of someone, and they turned their face from it, or closed their eyes, or it is at night [and they could not see it], or one is blind, it is permitted to recite [Sh'ma] for the Merciful One conditions it on seeing, and behold this is not seeing.