  The question of whether intelligent life exists elsewhere is one of the
fundamental unknowns about our Universe. Over the past decade more than 200
extra-solar planets have been discovered, providing new urgency for addressing
this question in these or other planetary systems. Independently of this
perspective, new radio observatories for cosmology are currently being
constructed with the goal of detecting 21cm emission from cosmic hydrogen in
the redshift range 6<z<15. For example, the Low-Frequency Demonstrator (LFD) of
the Mileura Wide-Field Array (MWA), will cover in 8 kHz bins the entire
frequency range of 80-300 MHz, which is perfectly matched to the band over
which our civilization emits most of its radio power. We show that this and
other low-frequency observatories (culminating with the Square Kilometer Array
[SKA]) will be able to detect radio broadcast leakage from an Earth-like
civilization out to a distance of ~10^{1-2.7}pc, within a spherical volume
containing 10^{3-8}x(Omega_b/4*pi)^alpha stars, where alpha=1 (or 1.5) for a
radar beam of solid angle Omega_b that remains steady (or sweeps) across the
sky. Such a radio signal will show-up as a series of narrow spectral lines that
do not coincide with known atomic or molecular lines. The high spectral
resolution attainable with the upcoming observatories will allow to monitor the
periodic Doppler shift of the broadcasted lines over the planet's orbital
period around the parent star. Determination of the parent star mass through
observations of its spectrum could then be used to infer the inclination,
semi-major axis and eccentricity of the planet's orbit. This, in turn, will
allow to estimate the temperature on the planet's surface and to assess whether
it can support liquid water or life as we know it.
