The Boundary Monitor is the component responsible for tracking player transforms and determining whether they cross specific boundaries. It communicates directly with Active Grid components in order to notify them when the grids associated Player crosses a boundary.
You can add this component by selecting a game object and then selecting from the Top Menu Bar:
Component -> Deep Space Labs -> -> SAM -> Secondary Components -> Boundary Monitor
or by selecting a game object and using the Add Component menu via its inspector:
Component -> Deep Space Labs -> -> SAM -> Secondary Components -> Boundary Monitor
The Inner Area Boundary of an Active Grid are the boundaries which trigger a shift of the Active Grid, which in turn can trigger a World Update.
When using World Origin Re-Centering, the Boundary Monitor also monitors a boundary which when crossed, triggers a world origin reset.