How Mouse Sentinel works with multiple monitors

Quick answer

Mouse Sentinel moves the cursor within whichever display currently contains it. Before each nudge, it finds that screen, calculates a small random offset, clamps the target at least one point inside the display boundary, and uses macOS cursor APIs to move there.

Why multiple displays are tricky

macOS treats connected screens as one extended desktop, but each screen has its own frame and can sit above, below, or beside another display. A monitor can also use a different scale or resolution. On top of that, AppKit and Core Graphics describe vertical coordinates from different origins.

A cursor mover that assumes one screen or one coordinate direction can jump to an unexpected location, hit a boundary repeatedly, or fail on a display arranged above the primary monitor.

Finding the active display

Mouse Sentinel reads the current pointer location and checks which macOS screen frame contains that point. That becomes the active display for the movement. The app does not intentionally transfer the cursor to another monitor during a normal nudge.

Choosing a small movement

Each movement uses a random angle and a distance between 8 and 28 points. The distance distribution favors a noticeable move within that small range. Mouse Sentinel also compares the new direction with the previous movement and tries to avoid a highly similar direction.

The purpose is modest variation, not human imitation. The app makes no “undetectable” claim and does not attempt to defeat monitoring systems.

Staying inside screen edges

After calculating the target, Mouse Sentinel clamps its horizontal and vertical position to the current screen’s frame, leaving a one-point inset. If the cursor starts near a corner, the resulting nudge remains within the usable screen boundary rather than disappearing beyond it.

Converting coordinate systems

AppKit mouse locations use a coordinate system whose vertical origin is at the bottom. Core Graphics display movement expects a display-local point measured from the top. Mouse Sentinel converts the target into the active display’s local coordinates before asking Core Graphics to move the cursor.

If the display-specific movement call fails, the app falls back to the system-wide cursor-warp API and posts a mouse-moved event. It then samples the pointer location to confirm that movement actually occurred.

What happens when you move the mouse

Mouse Sentinel monitors mouse, scroll, click, drag, keyboard, and modifier-key activity. When real activity occurs, it restarts the movement countdown. It briefly ignores its own generated mouse event so one automatic nudge does not indefinitely postpone the next one.

Why this detail matters

Reliable boundary handling makes a mouse mover less distracting and easier to predict. It also gives permission checks a meaningful result: Mouse Sentinel performs a tiny move-and-restore probe and reports success only if the cursor actually changes position.

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