The neutrino discovery, by Reines & Cowan, paved the technical ground behind the establishment of much of today’s neutrino detection. Large instrumented volumes can and have been achieved via a key (implicit) principle: detector transparency. Much of that technology has yielded historical success since the 50’s, including several Nobel prizes, where the discovery of Neutrino Oscillation by solving the long standing “Solar” and “Atmospheric” anomalies by SNO and SuperKamiokande — as well as many other experiments — is the latest example. Despite, the stunning success, much of the “transparent technology” is known to suffer from some key limitations. So far, no technology has fully solved them while keeping both the challenging large neutrino detector volume articulation and active background rejection. In fact, poor (or even lack of) native particle identification has been a long standing major issue. This limitation translates into the necessity for shielding for background reduction, including major overburden via underground laboratories as the only way to proceed. In this seminar, I shall discuss a new technology, under intense R&D, called “LiquidO” relying heavily on detection medium opacity for the first time. The effort is led by the LiquidO collaboration (20 institutions over 11 countries). We shall compare LiquidO to its transparent counterpart for maximal appreciation. While not perfect, LiquidO seem to offers several detection features that might lead to breakthrough potential in the context of both neutrino and rare decay physics. This will be briefly highlighted too.