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In Harry Potter and the Deathly Hallows, we find out when Ron returns to Harry and Hermione that Lord Voldemort put a taboo on his alias.

We see that this works in the chapter "A Place To Hide" when two Death Eaters find the trio near Tottenham Court Road after Harry says "Voldemort," so this taboo is already in place and working by later on in the same chapter.

After some debate, the crew decide to hide at Grimmauld Place; we know that there are certain enchantments to protect it against Snape already. Once inside, Harry's scar begins to hurt because of Voldy's anger, and Hermione says his name: "Otherwise Voldemort can plant false images in your head, remember." But no Death Eaters find them in Grimmauld Place.

Why is this? Have I missed something or did JKR make a mistake?

marked as duplicate by Valorum, Slytherincess harry-potter Nov 18 '14 at 23:45

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Grimmauld place is both unplottable and protected by the fidelius charm as well as other powerful protection magics:

‘It’s ideal for Headquarters, of course,’ Sirius said. ‘My father put every security measure known to wizardkind on it when he lived here. It’s unplottable, so Muggles could never come and call – as if they’d ever have wanted to – and now Dumbledore’s added his protection, you’d be hard put to find a safer house anywhere. Dumbledore is Secret Keeper for the Order, you know – nobody can find Headquarters unless he tells them personally where it is - Harry Potter and the Order of the Phoenix

After Hermione says "Voldemort", the Death-eaters seem to consistently hang around outside (they know there's something there) but they can't see the house or its occupants:

Barely a day passed without one or two people arriving in Grimmauld Place with no other purpose, or so it seemed, than to lean against the railings facing numbers eleven and thirteen, watching the join between the two houses. The lurkers were never the same two days running, although they all seemed to share a dislike for normal clothing. Most of the Londoners who passed them were used to eccentric dressers and took little notice, though occasionally one of them might glance back, wondering why anyone would wear such long cloaks in this heat.

The watchers seemed to be gleaning little satisfaction from their vigil. Occasionally one of them started forwards excitedly, as if they had seen something interesting at last, only to fall back looking disappointed. - Harry Potter and the Deathly Hallows

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