  Observational SETI has concentrated on using electromagnetism as the carrier
, namely radio waves and laser radiation. Michael Hippke [2] has pointed out
that it may be possible to use neutrinos or gravitational waves as signals.
Gravitational waves demand the command of the generation of very large scale
amounts of energy, Jackson and Benford [3]. This paper describes a beacon that
uses beamed neutrinos as the signal. Neutrinos, like gravitational waves, have
the advantage of extremely low extinction in the interstellar medium. To make
use of neutrinos an advanced civilization can use a gravitational lens as a
focus and amplifier. The lens can be a neutron star or a black hole. Using wave
optics one can calculate the advantage of gravitational lensing for
amplification of a beam and along the optical axis it is exceptionally large.
Even though the amplification is very large the dimeter of the beam is quite
small, less that a centimeter. This implies that a large constellation of
neutrino transmitters would have to enclose the local neutron star or black
hole to cover the sky. This means that such a beacon would have to be built by
a Kardashev Type II civilization.

Instrumentation and Methods for Astrophysics