SETI: A Critical History: Opening quote
"Even if these searches fail, that does not mean that we are alone.
The brains and senses of the aliens may be so different from ours
that we could not recognize any patterns in their signals ... The
only type of intelligence we could detect would be one that led to
a technology that we could recognize, and that could be a minor and
atypical fraction. Some 'brains' may have a quite different perception
– Martin Rees