If you have the engineers code go into engineer mode - this will suppress the tamper circuit. i am assuming you have magnetic contacts fitted to the existing windows. There will be 4 wires going to the contact (2 for alarm, 2 tamper) unscrew the contact and identify the 2 pairs, remove the alarm wires from the terminals and twist them together and wrap with insulating tape. Do the same with the tamper wires. The alarm will now simply see the detector as being closed circuit. Have a look at www.diy-alarms.co.uk it has some great info on alarms.
howard, May 2008