I have come across this article which I though qualified for a post here.
As some of you may already know it. It is possible to tap through a turned off mobile phone. More info on the subject read here and there.
Dan at this site has come up with a small technique to help prevent mobile tapping, to ensure total privacy… and all of this by just using a reed switch and a magnet.
Read more at http://www.stahlke.org/dan/phonemute/
If you are still not up for some soldering, you can always remove the battery from your mobile phone when not using it :)