A cellphone jammer. That'd be sweet. I'd mount it just outside my room, right where the Vile One frequently smokes while talking on the phone. With the area being a permanent dead zone, he'd move away and not bother me anymore.
But I'm not paying more than I did for my camera for a device that has just a single, specific use. And it could be illegal too.. not sure about the laws here.
And the house would still stink whenever he's here. It's a good idea, but not worth the risk and money.
Turning it on mid-conversation would be sooo satisfying, though. ^_^