Unlike most lizards, geckos are usually nocturnal and have excellent night vision; their colour vision in low light is 350 times more sensitive than human eyes. The nocturnal geckos evolved from diurnal species, which had lost the rod cells from their eyes. The gecko eye, therefore, modified its cone cells that increased in size into different types, both single and double.
Three different photo-pigments have been retained, and are sensitive to ultraviolet, blue, and green. They also use a multifocal optical system that allows them to generate a sharp image for at least two different depths. While most gecko species are nocturnal, some species are diurnal and active during the day, which has evolved multiple times independently.
Geckos are unique among lizards for their vocalisations, which differ from species to species. Most geckos in the family Gekkonidae use chirping or clicking sounds in their social interactions. Tokay geckos (Gekko gecko) are known for their loud mating calls, and some other species are capable of making hissing noises when alarmed or threatened. They are the most species-rich group of lizards, with about 1,500 different species worldwide. .