Originally Posted by Isoprop
Remove the two small screws at the "keychain" end and slide the bottom half (the one without the buttons) forward by lifting the two halves at the "keychain" end by max. 5mm. Don't lift the two halves apart any more or you may break the tags at the front of the casing.
You can't open the card slot without soldering, and I don't advise you to do that. There is a tiny spring (bar) inside the card casing which will spring out. It is so small it is barely visible and I guarantee you will lose it if you aren't very careful.
Thanks with your help I got it!