Loads a folder of videos and randomly plays them when triggered by a PIR sensor (or other trigger). Put this script in the same folder as the videos and launch. By default it will use *.mp4 as the filter. You can set the repeatcount if you want to play the same video specific number of times before the next random selection. While switching videos the desktop will be visible for a few seconds as omxplayer loads again. To mask that it takes a screenshot of the currently paused starting frame and sets it as the wallpaper. For this you will also need to install raspi2png to create the PNG file. There are also configurable delays (in seconds) for how long to wait between a motion trigger event and playing the video, how long to wait before switching videos, and for how long to wait before enabling the trigger again after a video finishes. Use these to enhance the startle factor by making it less predictable to passers by.
This version was developed on a Pi4 using the 2021-05-07-raspios-buster-armhf release. You need to use a Buster release that still has omxplayer in it as newer Raspbian releases don't work with it. This should still work on a Pi3B+ too, but I don't have one to test with.
For best results clear the desktop of all icons, empty the toolbar and set it to 0% opacity so it's invisible. That way between loading videos the screenshot wallpaper masks the fact that omxplayer is closing and re-opening to load next file. I also use unclutter in my startup to hide the mouse cursor.
ARGON ONE Users Note: The Argon One case uses GPIO 4 for it's internal power button, so you'll need to edit the motion sensor to use another GPIO pin. https://forums.raspberrypi.com/viewtopic.php?t=285383