Doesn't need to be big enough to scare people that badly. You could sneak a heap of something like this into any big concert venue pretty easily: https://www.

Doesn't need to be big enough to scare people that badly. You could sneak a heap of something like this into any big concert venue pretty easily: https://www.aliexpress.com/item/1005004496779816.html https://www.aliexpress.com/item/1005004496779816.html open them up and switch out the visible light LEDs for modulated IR ones, add a tiny microcontroller to send pre programmed data. Get you and a dozen friends to launch them all at the same time...