pxt-calliope/docs/reference/input/on-gesture.md

On Gesture

Start an event handler (part of the program that will run when something happens) This handler works when you do a gesture (like shake, tilt, or drop the micro:bit).

input.onGesture(Gesture.Shake,() => {
})

Example: random number

This program shows a number from 0 to 9 when you shake the micro:bit.

input.onGesture(Gesture.Shake,() => {
    let x = Math.random(10)
    basic.showNumber(x, 100)
})