The eBay description is "normally closed"
To my way of thinking that means the contact is closed without any outside influence (eg magnet).
When the magnet is adjacent to the contact, the contact will open.
Try this link
http://www.cameuk.com/camenew/tech-docs/02_Control%20panels/ZA3_319S13/S13v31-1.pdf
There is a Nottingham telephone number at the bottom of the pages