Privacy (tzni’ut; lit. “hiddenness”) is an expression of the sanctity of the mitzva of ona; Rashi explains the Sages’ exhortation to sanctify oneself: “Engage in sexual relations in a private manner” (Nidda 71a). This precious mitzva is meant to express the complete unity between husband and wife, so it is forbidden to expose it before others, and it is forbidden for others to discuss it. Every couple has its own special way of being together, which encompasses a whole world. Any couple lucky enough to be madly in love feels that there is nothing else like their love in the whole world. The Kabbala likewise explains that at the moment when husband and wife achieve true unity, light and blessing spread through all the worlds. Since their union is so profound, it should be kept like a secret between them.
Sexual intimacy must therefore take place at home or in an enclosed, private area. It is forbidden to have intercourse in public or in an open space, even if there is no one there to see it. Those who do so look like they are behaving promiscuously and habituating themselves to sinfulness, for which they deserve to be punished (Sanhedrin 46a; SA EH 25:4). It is forbidden to have sexual relations in the presence of any other person, even someone who is sleeping, for they may wake up. Technically, a couple may have sexual relations in the presence of a preverbal baby; however, this, too, is inappropriate, and is therefore permitted only when there is no other option, and when the baby is sleeping. If the baby wakes up while the couple are still having intercourse, they may continue. Le-khatḥila, there should not be pets, such as dogs or cats, present.
It is customary for the couple to be under covers during sexual intercourse, even where there is no light (see Darkhei Tahara 22:39).
The couple must keep the time of their sexual relations private. During intercourse, they should be careful that their voices cannot be heard by others. It is also proper for the wife to be discreet about when she goes to the mikveh, so that no one will sense that she is going (Rema, YD 198:48).
To ensure that intimacy takes place joyfully and in private, without concern that children or guests might suddenly enter the room, the couple should make sure to lock the door to their room. They should do so every night when they go to sleep, so that it is not obvious when they are fulfilling the mitzva. They should also not let one of the children sleep in their room.
Husband and wife should not tell others about their lovemaking practices. Only when necessary, to seek guidance and obtain advice, may this information be divulged. Furthermore, a couple may not speak about their intimacy in a coarse or foul-mouthed manner, such as in the manner of those who tell dirty jokes (MT, Laws of Dispositions 5:4).It is likewise forbidden to talk about anyone else’s sex lives unnecessarily, and all such talk is considered nivul peh (vulgar, explicit, or foul language). It transforms vibrant discussion whose purpose is to increase blessing into repulsive, dead speech. Such talk can be compared to a decaying carcass (nevela), which is forbidden to eat. The Sages say, “Everyone knows why a bride enters the ḥuppa, but if someone speaks about it in a vulgar manner, then even if the heavenly court had sealed a decree of seventy good years on his behalf, it will all turn bad on him” (Shabbat 33a).
Guests may have sexual relations as long as they have a closed room, there is no concern that the hosts will be aware of it, and they leave no evidence on the sheets.
It is proper for a couple to refrain from behaving in a way that expresses their desire for one another in front of others (Rema, EH 21:5). A polite hug or kiss, in a society where this is considered acceptable, is not a breach of modesty, but if it expresses sexual desire, it is immodest, for the love between husband and wife is a very deep and personal matter. Exposing it in front of others trivializes it and cheapens it. The couple should also be sensitive to the fact that such displays of affection can cause pain and stir up jealousy among those who are not privileged to be in such a relationship.
Matters of modesty and privacy are dependent upon accepted norms. Therefore, in the past, when homes were smaller and sometimes an entire family lived in one room, parents were allowed to be sexually intimate while their children (and anyone else in the room) were sleeping. Moreover, in those times, people generally slept more soundly, since they worked at hard physical labor all day. However, now that homes have several rooms, norms of privacy dictate that sexual intimacy is forbidden in a room where someone else is sleeping. See Harḥavot 13:5-6. It is worth adding that locking their bedroom door not only allows a couple to fulfill the mitzva with great joy, but it also has educational value in that it teaches the couple’s children how deep and personal their parents’ relationship is, and that it must not be disturbed. They will thus learn by example how to live accordingly, and they will merit establishing good families of their own.