Commensal searches for extraterrestrial intelligence with Arecibo Observatory and the Green Bank Telescope

Our group is currently developing two new instruments to conduct commensal searches for extraterrestrial intelligence (SETI) at the Green Bank Telescope and Arecibo Observatory. The SETI sky surveys conducted with these two instruments will use all available receivers at these two facilities and target a range of signal types. When complete, these surveys will be the most sensitive and thorough sky surveys for radio emission produced by extraterrestrial technology ever conducted. Here we describe the technical details of our new digital instruments, including the signal acquisition, distribution and science processing components. We also discuss expected science returns and potential expansions to the digital system that could enable wider bandwidths and allow other observers to use the system for their own commensal programs with a minimal investment in new hardware.