SETI is based on the hope & belief that life exists elsewhere, that it is intelligent in the way we understand it, meaning communication and technology, that it likewise believes in extraterrestrial life, that the radio bandwidth is meaningful to it as it is to us, that it would be broadcasting in our direction of the universe, and that it has been doing so say within the few hundred years. So, the radius which we can search is limited by sensitivity of telescopes here, and also transmission power on the other end. That last one is a complete unknown as are all the other assumptions I listed here. SETI is a high-risk project which is probably worthwhile doing (we have to start somewhere), but ever finding anything would be unbelievable luck - we just don't know what's out there.

LIGO otoh is a realistic project - to detect the gravity waves predicted by the Einstein equations - but it's still risky in that we can't absolutely say for certain yet, that these really exist and are not just mathematical artifices in General Relativity .. the risk is good, very much more meaningful than SETI, since we have the confidence of GR as a working physical theory, and not just a mathematical artifice, and we have experience (since Maxwell's EM equations) in predicting physical phenomena directly from the maths, rather than through experiment. E = mc-squared was a purely theoretical result, which came directly out of Special Rel, ie. considerations of nothing more than uniform motion at high relative speeds .. Einstein didn't see the full physical potential, at first he thought only in terms of an object losing mass while releasing or transferring energy. Similarly with quantum mechanics - this bizarre mathematical theory is the basis for semiconductor and solid-state physics

The US has led the way in GW detection with LIGO which has 2 interferometer detectors in the US, like this one at Hanford -

and there are other observatories in Italy, Japan, and a smaller one in Australia, where I spent a few weeks early last year. Also, I heard the Chinese are interested in building a LIGO-type detector ..

So the risk (trusting the maths) is low-to-medium at worst, especially since we have such strong 'circumstantial evidence' - but it's not zero, as we just don't yet know for sure. If we can find gravity waves the theory predicts we will hear them in the human audio bandwidth .. which is incredible when you think about it - without having to transpose the pitches (as we do with solar oscillations, bunging them up 20 octaves to our hearing range) we could directly hear the sounds of the universe, as if in a gigantic forest ..

GR and GW is a better bet than SETI .. but the detectors are still about 100 times too 'insensitive' to react to expected strains in space of 10-to-the-minus-23 meter .. this sensitivity is expected for next-generation LIGO in a few years time. In the meantime looks like they're making best possible use of the existing data with the Einstein@home initiative .. I hope they get lucky ..