If you attend a public menorah lighting such as what Chaba"d does by lighting the huge "Central Park" menorah, Shulchan Arukh, Orach Chayyim 676:3 says:
מִי שֶׁלֹּא הִדְלִיק וְאֵינוֹ עָתִיד לְהַדְלִיק בְּאוֹתוֹ הַלַּיְלָה,
וְגַם אֵין מַדְלִיקִין עָלָיו בְּתוֹךְ בֵּיתוֹ, כְּשֶׁרוֹאֶה נֵר
חֲנֻכָּה מְבָרֵךְ: שֶׁעָשָׂה נִסִים, וּבְלֵיל רִאשׁוֹן מְבָרֵךְ גַּם:
שֶׁהֶחֱיָנוּ, וְאִם אַחַר כָּךְ בְּלֵיל ב' אוֹ ג' בָּא לְהַדְלִיק
אֵינוֹ חוֹזֵר וּמְבָרֵךְ: שֶׁהֶחֱיָנוּ.
Someone who has not yet lit, doesn't plan to light and has no one in his household who will light for him that night (i.e., all 3 conditions must be met) will recite the 1st 2 blessing on all nights and on the 1st night, he adds the 3rd blessing when he SEES the menorah being lit...
I'm inferring from this, that if any of these conditions will be met, he will not recite any blessings when seeing the public lighting, but will say them at home or will have fulfilled the obligation if someone else has lit for him. (I.e., he doesn't need to be home at the time someone else in his home lights.)