Your screen shouldn't dim mid-slide
You're giving a presentation. You've been on the same slide for a few minutes while you explain something. The screen dims. You jiggle the mouse, it comes back, and you try to pretend that didn't just happen. Everyone noticed.
This is one of those things that feels like it shouldn't happen. You're actively presenting. The app is in fullscreen. Shouldn't macOS know better? Sometimes it does. But often it doesn't, and the situations where it fails are exactly the ones where it matters most.
Why Keynote and PowerPoint don't always prevent it
Both Keynote and PowerPoint are supposed to request a sleep assertion when you enter slideshow mode. In theory, macOS sees this and keeps the display on. In practice, there are gaps.
External displays are the biggest culprit. When you're presenting on a projector or TV via HDMI or AirPlay, the sleep assertion sometimes applies to the wrong display, or doesn't fire at all. If you're using Presenter Display mode (where your notes show on the MacBook and the slides show on the projector), the behavior gets even less predictable.
Switching apps mid-presentation also breaks things. If you tab over to a browser to show a demo or open a PDF, you've left the slideshow app. The sleep assertion goes away. Your idle timer starts counting down. A few minutes of demoing something outside Keynote, and the screen dims.
The fix: Shake It On with scheduling
Shake It On keeps your Mac awake by generating mouse movement, which resets the idle timer regardless of which app is in the foreground. It doesn't depend on any specific app requesting a sleep assertion, so it works whether you're in Keynote, a browser, or a PDF viewer.
For presentations, the most useful features are:
- Scheduling. If you present during regular business hours, set Shake It On to run on weekdays from 8 AM to 6 PM. It'll keep your Mac awake during those hours and sleep normally outside of them. No toggling needed.
- Paused When camera is in use. This one's smart: if you're on a video call (Zoom, Teams, Meet), the camera condition detects it and pauses shaking. You probably don't need mouse jiggling during a video call since those apps handle sleep prevention on their own. When the call ends and you switch to presenting, shaking resumes.
Setup tip for presenters
Set the shake interval to something short, like every 2-3 minutes, and keep the distance small (10-15 pixels). During a presentation, you want the idle timer reset frequently enough that the screen never dims, but you don't want the cursor visibly jumping around on the projector.
If you're presenting on an external display and worried about visible cursor movement, park the cursor in a corner of your MacBook's screen before you start. Shake It On moves the cursor on whichever screen it's currently on, so the projector audience won't see anything.