Bluetooth and most WiFi signals operate on the 2.4 GHz band. Most everyday cordless phones work on the same 2.4GHz frequency. Therefore, with a little tweaking you can turn a cordless phone into a Bluetooth and WiFi jammer. (This device will only jam WiFi routers that operate on the 2.4GHz band. Routers that use 3.7Ghz [...]

Jammers are illegal in England, the United States and most of the European Union. But the most basic jammer costs as little as fifty dollars in Hong Kong. By sending out a blizzard of radio waves, this cigarette packet-sized gadget will knock out a mobile phone signal within a radius of five to ten yards. [...]