In the Odyssey, the Sirens are two creatures whose song enchants those who pass nearby and makes them forget the way home. Odysseus is the only one who hears them and survives: he follows Circe's advice, orders his companions to plug their ears with wax, and has himself tied to the ship's mast, standing, so as to listen without being able to throw himself into the sea.
The warning comes from Circe, in Book XII. She says that whoever hears the Sirens in ignorance is never again welcomed home by his wife and children, and that in their meadow there are the bones of men rotting. If Odysseus wants to listen, his companions should bind him "hand and foot" to the mast and, "if you beg your companions to release you," they should tie him with even more bonds. Odysseus repeats the order to the men, cuts a large disc of wax, kneads it, smears the ears of all, and gives himself up to the ropes.
What the Sirens sing is an offer of knowledge. They call him by name and say that no one has passed there without hearing them and that whoever hears them "goes away delighted and knowing more." They know everything that Greeks and Trojans suffered in Troy and everything that happens on the earth. Odysseus's heart wants to hear, and he signals with his eyebrows for them to release him, but Perimedes and Eurylochus stand up and tighten the ropes even more. Only when the song fades into the distance do the companions take the wax from their ears and untie him.
The scene gathers what the poem thinks of Odysseus. He is curious, wants to hear what no one has heard, and has the cunning to foresee his own desire and protect himself against it. The temptation is not a woman or a treasure, but knowledge. The price of yielding would be the loss of the return, and it is the obedience of his companions that prevents it. Right after come Scylla and Charybdis, the danger that has no solution by cunning, and Odysseus loses six men.