Less than $2, just get one some of these... https://www.aliexpress.com/item/Free-shipping-1pcs-Digispark-kickstarter-development-board-ATTINY85-module-for-Ardu

Less than $2, just get one some of these... https://www.aliexpress.com/item/Free-shipping-1pcs-Digispark-kickstarter-development-board-ATTINY85-module-for-Arduino-usb/32697283942.html?spm=2114.search0104.8.29.2h1SOp https://www.aliexpress.com/item/Free-shipping-1pcs-Digispark... Wack a buzzer on them, add some code and then leave them in a usb port near your victim. Easy.