9448, how do i silence the external alarm?

Hi, I need to turn the power off to the house for a job, but when I knock the power off, the outside sounder goes off on my 9448 (think I have the 9427 panel). I have input the code, but it wont stop the outside buzzer unless I put the power back on, then the internal buzzers sound too but the code will reset them. Is there any way that I can silence the outside buzzer while I work with the power off? Many thanks craig