Hesach Hadaas when Wearing Tefillin

While wearing tefilin, one should constantly be mindful of the fact that he is wearing them, except during Shemonei Esrei and Torah learning, when he needs to focus instead on those activities. Taking his mind off his tefilin while wearing them, even for a moment, is referred to in halachah as hesach hada’as. Whereas constantly being cognizant of his tefilin is the preferred mode of behavior, the actual prohibition of hesach hada’as applies only to being involved in anything inconsistent with the spirit of tefilin, such as laughter, idle talk, anger, or depression. However, if one is occupied with mundane activities while wearing tefilin and not consciously focusing on his tefilin, but is nevertheless mindful of the fear of Heaven, it is not considered hesach hada’as. If his mind begins to wander, he should touch his tefilin to remind himself that he is wearing them, and thereby get back into the right frame of mind. Thus he will prevent himself from falling into total hesach hada’as and focusing on things which are inappropriate for one who is wearing tefilin.

https://halacha2go.com?number=195

Practical Halacha: One minute a day. By Horav Yosef Yeshaya Braun, shlita, Mara D'asra and member of the Badatz of Crown Heights.