Newlywed Shira and Shlomo Stern traveled out from Twin Oaks Drive in Lakewood NJ to Cincinnati, Ohio for a friend's wedding. Shlomo's sister and brother-in-law Ayala and Ari Greenberg lived in Cincinnati but were en route to Eretz Yisrael to spend Lag Ba'omer in Meron.

The Greenbergs were overjoyed to allow Shira and Shlomo to stay in their empty home for the extended weekend. After settling in, the Stern's began to ready themselves for the wedding when Lo! Shira realized that she wanted to daven Mincha and...forgot her Sheitel in Lakewood.

Her teary eyes fell upon Ayala's Sheitel neatly perched on her High Gloss Dark Brown Cherry Finish Eight Drawer Dresser with her large Burgundy colored leather-bound Korban Mincha Siddur laying nearby.

Ayala was in the air...

 

Unless having received express permission, Shira may presumably not use Ayala's Sheitel.

See Detailed Explanation for whether she may use the Siddur.

 

 

People are happy for other's to perform mitzvos with their property [Tractate Pesachim 4b, Orach Chaim 14: 4].

Do not use someone's sefer Torah without permission [Tractate Bava Metzia 29b, Choshen Mishpat 292: 20].

In the words of the Shulchan Aruch, as long as one folds up the Talis properly and takes care not to ruin the Tefillin, if one enters a Shul and finds Tefillin or Talis on the table and needs to use it, if there is no reason to assume that his friend would need it then, he may use his friend's Talis and Tefillin without receiving explicit permission because there is implicit permission that one Jew would want another Jew to perform a mitzvah with his/her belongings so long as there is no significant risk to the article.

In previous times when seforim were rare and pricey, there was no implicit permission for the general populace to use other people's seforim.

Exceptions would include if A deposited a sefer in the hands of a Talmid Chochom for safeguarding, there was implicit permission for the Talmid Chochom to use the article.

Nowadays, however, the factors have changed. Seforim are not rare and pricey and generally people give implicit permission to permit others to use their seforim when they do not need them so long as they do not put the sefer at risk of damage or loss.

If however, there are reasons that indicate that the owner is particular about others using them; for instance, he/she locks them in a private cubby in shul, then it is clear that the owner does not give implicit permission for others to use it without his/her knowledge.

Tefillin on the other hand are expensive nowadays. Enough people are particular that others should not use their Tefillin without their knowledge to require one to air on the side of caution and not indiscriminately use another's Tefillin without permission, unless there is a clear indication that the owner permits you to use it without his knowledge.

Regarding a Talis, enough people are particular about other's sweating into their Talis that one would not be able to indiscriminately use another's Talis if he is sweating. The same would apply if the Talis is new or put away in one's private cubby.

A Siddur which is not put away in a private cubby? Generally, nowadays so long as one is not using it when the owner might need it, people do not mind for others to use it. However, if you have reason to assume that the owner might be particular, for instance the owner might write personal prayers or information inside, do not use it without express permission [Orach Chaim 14: 4, Aruch Hashulchan 14: 12, 13, Choshen Mishpat 292: 20].

Thus, bottom line remains the same:

One may not use another's belongings without his knowledge (or implicit permission). (See Issue 231 for possible other exceptions)

We can arguably assume that Ayala is highly particular about lending out her Sheitel to her sister-in-law. Thus, Shira's intent to use it for a mitzvah does not give her the license to use it.

A Siddur on the other hand can generally be assumed to fall into the category of items which people permit others to use carefully for a short time, especially if Ayala is permitting Shira to use her room.

If Shira does think that perhaps Ayala writes personal notes inside her Siddur, then she should not use it.