When something is detectable, you can notice it or find it — even if it is small, quiet, faint, or trying not to be seen. We use it a lot with tests and machines: a smell that is barely detectable, a leak that is detectable only with a special tool, a disease that is detectable in a blood test. Though actually, detectable does not mean “easy to notice.” It only means “possible to notice.” Something barely detectable is almost not there; you need a careful look, or a machine, to catch it. The word is common in science, news, and safety talk, and it sounds a little more careful than “you can see it.”