Disconnecting an Optima XM system?

My Aunt bought a house almost 10 years ago with an Optima XM alarm system already built in. She's now 80 years old with a heart and high blood pressure condition and although she's never set or used the alarm -- it does periodically go off when there's an unexpected electrical outage or surge.

This happened twice last night and I'm afriad she'll die of a heart attack if I can't find a way to permenantly disconnect the system. I'vr read the manual and I know it's wired into the mains but am afraid it's tamper resistent systems may set it off if I try to disconnect it.

Can anyone give me step by step guidance on how I would go about disconnecting this permenantly from the mains?