Neŭtrino detectors are coming along nicely! For example, see this paper on the compact COHERENT detector, which is theoretically portable! https://arxiv.org/pd

Neŭtrino detectors are coming along nicely! For example, see this paper on the compact COHERENT detector, which is theoretically portable! https://arxiv.org/pdf/1708.01294 https://arxiv.org/pdf/1708.01294 It can only detect neutrinos <50 MeV but still, wow. Production, modulation and beam forming (and then demodulation and background removal) is a significant challenge, but neutrinos have many advantages for signaling for a galactic civilization, such as not needing to worry about occlusion.