One night going to the bathroom I noticed a small but cold draft. I was passing the doors the our children's bedrooms. They sleep with their windows open at night and this was a windy night. So I could feel this draft, but their door to the hall was closed. This puzzled me, but as I got closer to the door, I realized that the draft was coming out of the key hole! I used a piece of tape to stop the draft. It is almost invisible to the eye, and does help. It is common knowledge that any drafts must be stopped. No point in adding much new insulation to your house if the cold wind is blowing through it any how. In our living room I have also insulated the keyhole. Here I have used a bit of black electrical tape on the inside of the hole, and also a bit of insulation material behind that. This door separates our home movie theater from the rest of the house. So here the motivation was originally to sound proof the door, but it works for draft proofing as well.
Summary in Norwegian: På natten sover vi med åpne vinduer og dørene stengt til resten av huset. En vinter natt på vei til toaletet merker jeg at det kom iskaldt trekk i gangen. Det kom fra nøkkelhullet! En tape fixet problemet. Dette understreker hvor viktig det er at man finner kilder til trekk i huset og så tetter dem. Det kan like gjerne være en skjev dør eller dårlig tetting rundt vinduer som lager trekk.