Chazal tell us that answering “amen” is mesugal for arichus yamim (longevity), but there are two “amens” that are particularly conducive for long life.

They are the “amen” answered after המחזיר שכינתו לציון and the “amen” after הפורס סוכת שלום (said in Maariv of Shabbos and Yom Tov).

~ R’ Liber HaGadol of Berditchev zt”l

I will just add that the Satan must know this, as it seems people often skip answering amen to these two brachos, rushing into “Modim” or “V’shamru.” Be mindful and careful not to miss them.