With the bitty audio prank app on your smartphone or tablet you can make it emit surprising and funny sounds just by pressing buttons on your BBC micro:bit in various ways.
Communication between the micro:bit and smartphone is wireless using Bluetooth so you could hide your smartphone in a room and have fun watching friends and family react when they hear unexpected sounds coming from unlikely places :-)
The associated micro:bit coding tutorial, which you can use free of charge at http://www.bittysoftware.com, will teach you how to write micro:bit software which responds to buttons being pressed, how to detect the physical orientation of the micro:bit, about micro:bit "events" and about the micro:bit Bluetooth "event service".