But it only works in Iceland:

"A new smartphone app is on hand to help Icelanders avoid accidental incest. The app lets users "bump" phones, and emits a warning alarm if they are closely related. "Bump the app before you bump in bed," says the catchy slogan."

http://www.oregonlive.com/today/index.ssf/2013/04/smartphone_app_helps_icelander.html#incart_river_default