"Mike Williams" <nospam@econym.demon.co.uk> wrote

However, omnidirectional broadcasts would be extremely unlikely to be
strong enough to be detectable at interstellar distances. We should only
realistically expect to spot narrow beams that are pointed in our
direction.

Agreed, continuous omnidirectional broadcasts would have to be extremely
powerful to be detectable. But to say that is a problem presumes a
technology analogous to our own i.e. a power source and a broadcast antenna.
It's not inconceivable that an advanced civilization might be able to
harness or modulate a star or other powerful natural source. The point is,
we just don't know, and worse we don't know what we don't know.

Cheers.