Is one permitted to sleep while holding tefillin?

It is forbidden to take a nap while wearing either the shel yad or shel rosh. If one sees another person sleeping while wearing tefillin, he must awaken him. It is also forbidden to sleep while holding tefillin, as there a concern that they may fall to the floor. If they are in a case or bag, they may be held, since it is not a tremendous disgrace if they fall to the ground that way. Some Achronim add that the case must be large enough to contain a tefach of space that could serve as a separation between the floor and the tefillin.

סימן מד, סעיף א וס"ק ד, ז ו־ח; ביאורים ומוספים דרשו, 9

Is it permissible to run a business while wearing tefillin?

It is forbidden to be masiach da’as (lose focus) from the tefillin while they are being worn. The poskim explain that hesech hada’as occurs when one acts with levity and lightheadedness. Mundane day-to-day activities are permissible while wearing tefillin, however. If a person is involved in mundane tasks, he should be certain to touch his tefillin from time to time in order not to be masiach da’as. It is not necessary to touch the tefillin while davening or learning.

סימן מד, ס"ק ג וביה"ל ד"ה ישן; ביאורים ומוספים דרשו, 4-3  

Can tefillin be worn in a cemetery?

It is forbidden to wear tefillin within four amos or less of a dead body or grave. Doing so mocks the deceased, who can no longer keep mitzvos. Tefillin should not be worn in the middle of a cemetery, either, even if one is not within four amos of a grave. Tefillin can be worn at the edge of a cemetery, provided that one is not near a grave. Nevertheless, a person should refrain from doing so, since he may end up walking into the cemetery. Tefillin should not be worn near the grave of a child, and the poskim disagree about whether the same applies to the grave of a woman.  

סימן מה, סעיף א, ס"ק א-ב, וביה"ל ד"ה אסור; ביאורים ומוספים דרשו, 2

• It is permitted to bring tefillin into a bathroom if they are encased in a double covering. One of the covers cannot be its dedicated case. Some poskim allow papers with divrei Torah which do not have any holy names of Hashem on them to be brought in with just one cover.

• The poskim disagree about whether printed sifrei kodesh and divrei Torah must have two coverings in order to be brought into the bathroom or whether one cover would suffice.

• In earlier times, there were areas known as mavo’os metunofos (unclean alleyways). These alleys or streets were filled with filth, and it was forbidden to think Torah thoughts when walking through these areas. The Achronim disagree about whether one could walk through these streets while wearing uncovered tefillin.

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