Which button do you have to press to activate the security alarm and how many seconds do you have to hold it for?
この場合、次のような言い方ができますよ。
ーWhich button do you have to press to activate the security alarm and how many seconds do you have to hold it for?
「防犯ブザーを鳴らすのにどのボタンを何秒間押さないといけないの？」
to activate the security alarm で「防犯ブザーを作動させる・鳴らす」
ご参考まで！
カナダ 
