Fear Campaign

Is it true that you can scare people into "healthy" behavior? There are two ads doing the rounds at the moment which try to Scare people into either not smokirg or not using their mobile phone while driving. The anti-smoking ad shows a man's gangrenous leg about to be removed. The mobile phone one has a woman drive reaching to get a ringing mobile phone and when it appears in frame it is a gun that she goes to point at her temple. The ad has the super "Dead Ringer". But do these scare tactics work? Or do people think "that won't happen tome" and actively block the message?