Find units in a ring constituted by Gauss integers.

So I know that Gauss integers are $\displaystyle a+bi \ \ \ a,b \in \mathbb {Z} $[/tex]

Now, of course $\displaystyle -1, 1, i, -i $ are units, but would $\displaystyle 1-i,-1+i$ also be units? And are there anymore?