Entering in mid-kedushah

Hi,

One who enters the synagogue in the middle of Kedushah should respond appropriately to the lines he hears; he should not recite the parts that he missed.

(Rivivot Ephraim 1:90)

Have a great day,
Mordechai

Answering Kedushah from outside the room

Hi,

One who is outside of a room in which a minyan is davening should answer Amen and recite the responses to Kedushah. However, one who has already davened, and is in a space from which he can hear many minyanim, is not obligated to remain there in order to respond to all of them.

(Rivivot Ephraim 1:89:1)

Have a great day,
Mordechai

The chazan's "Kedushah"

Hi,

The chazan should say "Kadosh kadosh" and the other key lines of Kedushah along with the community, and not wait to say them until after the community has concluded saying them.

(Rivivot Ephraim 1:87)

Have a great day,
Mordechai

Answering berachot before Birchot haTorah

Hi,

We are supposed to recite Birchot haTorah (blessings upon Torah study) each morning, before learning any Torah. However, one who hears a berachah may answer Amen before reciting these berachot. One also may answer Kedushah before reciting these berachot, even though the responses are themselves biblical verses.

(Rivivot Ephraim 1:39:1)

Have a great day,
Mordechai

The Chazan's recitation of Kedushah

Hi,

The chazan should state the responses of kedushah [Kadosh Kadosh, Baruch Kvod, Yimloch] aloud, separate from the community's recitation of those responses. In this way, he will fulfill the obligation of individuals who have not yet completed the amidah, who then listen to his responses as their own.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 3:4)

Have a great day,
Mordechai