My system is a MacBook Pro late 2013 running macOS Sierra 10.12.6.


  • Occasionally after the laptop wakes from sleep, the system would behave as if someone is repeatedly pressing a certain key on the keyboard.

  • If I click anything (Apple icon, File, Edit...etc) on the menu bar, the item whose name starts with A will be highlighted repeatedly, B if nothing starts with A, and so on. (Therefore, I assume the keystroke being sent is a number.)

  • If I press cmd+tab attempting to switch between apps, the focus will automatically scroll all the way to the right-most item.

  • This doesn't affect all apps. I am able to use Chrome as if there's nothing wrong.

My question:

  • Apparently one or more of the processes running on my system is doing this. To find out which process / app is sending the keystroke, I am looking for a way or a tool to monitor who is sending keystroke. Therefore next time this happens I can use this to determine the culprit.


  • Is it possible your keyboard is malfunctioning, or there's another keyboard connected (maybe a Bluetooth wireless keyboard)? – Gordon Davisson Apr 15 '19 at 6:49
  • I don't have any Bluetooth keyboard and the only Bluetooth devices I use are headphones, which are usually not turned on when this happens. It doesn't feel like a hardware malfunction because it only happens, occasionally, after waking up from sleep. If it was a keyboard issue, I think I would notice it more frequently and not only after sleep. – Vic Jang Apr 15 '19 at 18:34

It turned out that the culprit was Karabiner-elements, and the issue has been resolved in the latest update.



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