Rhodopsins are ancient and evolutionarily conserved light receptors. Based on >100 years of study, the dogma was that they function exclusively in light reception. Our recent and ongoing work in fruit flies, mosquitoes and the mouse challenges this tenet. We uncovered the first light-independent role for these evolutionarily conserved light sensors in fruit flies. Remarkably, opsins enable fruit flies to discriminate between tiny temperature differences within the comfortable range. Our recent results identify additional, light-independent functions for opsins in taste and other senses, leading us to propose that opsins function in all senses where, as in the visual system, they confer great sensitivity to weak stimuli as well as the capacity to adapt. We propose that these properties of opsins help animals from flies to humans detect exquisitely minor levels of sensory stimuli, and then respond appropriately.