  Let $(A,\sigma)$ be a central simple algebra with an orthogonal involution.
It is well-known that $O(A,\sigma)$ contains elements of reduced norm $-1$ if
and only if the Brauer class of $A$ is trivial. We generalize this statement to
Azumaya algebras with orthogonal involution over semilocal rings, and show that
the "if" part fails if one allows the base ring to be arbitrary.
