Why gecko hiss?

Leopard geckos hiss as a defence mechanism. If you pet leopard gecko is hissing at you, it is probably not tame yet. Taming them takes time, but it's fairly easy. Pick him up (if he bites, you could wear a heavy gardening glove ) and handle him 15-20 minutes a day, twice a day. Don't pick him up by his tail, or he'll release it, and look ugly for the rest of his life.