How do I open the system to get to the battery?

The battery is located inside the panel.

Insert a flat blade screwdriver into the slt at the top (front) of the panel and release the catch. The panel will fold down to reveal the PCB panel, the battery and the cabling connections for hardwired sensors, telephone & 9V AC power supply.

The battery has push connectors that can be unpluged for replacement.

Replacement batteries are available from your dealer or via Online security store specializing in GE Simon products.