Let's find the limit:
[tex]\begin{gathered} \lim _{x\to-\infty}(2^x+1)=\lim _{x\to-\infty}2^x+\lim _{x\to-\infty}1 \\ where\colon \\ \lim _{x\to-\infty}2^x=2^{\lim _{x\to-\infty}x}=0 \\ so\colon \\ \lim _{x\to-\infty}(2^x+1)=1 \end{gathered}[/tex]Therefore, the horizontal asymptote is:
[tex]y=1[/tex]