I am going to pressumeit is a basic alarm panel - but still this will work. On the door should be a magnet and on the frame will be the other side a reed contact. un-screw both units and tape - cello tape or elastic band - to hold the two items together. to test try setting the alarm see if it will fully set. I f all is well then pull back anough to give the new door fitters romm to install the new door. /IOnce the dooe=r is back refit it as it is now but on the new door.
Mark
May 2011