French researchers have developed wallpaper that's designed to trap Wi-Fi signals, without interfering with radio or cellphone signals. It uses conductive ink containing silver crystals to to block a Wi-Fi router's operating frequencies: your router should work as expected, but the signal won't travel beyond the wallpaper's boundaries. While currently only a prototype, researchers at the Grenoble Institute of Technology hope to make the wallpaper commercially available early next year.
An earlier variant of Wi-Fi-blocking wallpaper was developed by a British defense contractor back in 2004, but it cost upwards of £500 per square foot — well out of the comfort range of your average homeowner. The researchers at Grenoble Institute claim that their solution will cost as much as conventional, mid-range wallpaper, though they haven't quoted a particular price range. This technology could add an extra layer of protection, but it isn't foolproof: you'd need to cover your walls, ceiling, and floor with (admittedly attractive) snowflake patterns for full coverage. There will also be gaps in protection at windows and doors, though the researchers have expressed plans to develop transparent variants of the technology.