  We prove analogs of faithfully flat descent and Galois descent for categories
of modules over $E_{\infty}$-ring spectra using the $\infty$-categorical
Barr-Beck theorem proved by Lurie. In particular, faithful $G$-Galois
extensions are shown to be of effective descent for modules. Using this we
study the category of $ER(n)$-modules, where $ER(n)$ is the
$\mathbb{Z}/2$-fixed points under complex conjugation of a generalized
Johnson-Wilson spectrum $E(n)$. In particular, we show that $ER(n)$-modules is
equivalent to $\mathbb{Z}$/2-equivariant $E(n)$-modules as stable
$\infty$-categories.
