Howdy! I made this tool because I found I almost never remember to lock my iMac when I step away from it. But I also noticed that I almost always left my Yubikey plugged in, and being attached to my keychain, I would also always remove it when I walked away. So I wrote an app to leverage that behavior. You can pick almost any USB device plugged into your Mac (I try to filter out all of Apple's built-in hardware and USB hubs), and trigger either the screen to lock, or the screensaver to start (you really should require a password to stop the screensaver, of course) upon removal. I'm planning on adding support for plugged in headphones, and possibly Bluetooth in the near future, and would love your feedback on what should be next.