Another current SETI program
is
optical SETI,
in which distinctive visible-light signals appearing to come from other stars
are sought. Other similar programs are being
carried out at
Lick
Observatory and at
Harvard.
These programs are all looking for optical light -- lasers --
not for radio waves (like the Arecibo searches).
There is an important philosophical distinction: the
radio searches could (in theory) detect "accidental"
transmissions from an advanced society, in addition
to purposeful messages [more on that in a minute].
On the other hand,
the optical searches would basically detect
only purposeful laser emissions from other
civilizations
(because optical light gets absorbed by
interstellar dust, but radio waves do not).
The optical SETI searches therefore are
predicated on the idea that someone
out there is sending targeted laser beams
into space. Note that WE are NOT doing that.