Take screenshots in simulator with S key

main.lua

if app.isSimulator then
    Runtime:addEventListener('key', function (event)
        if event.keyName == 's' and event.phase == 'down' then
            local scene = storyboard.getScene(storyboard.getCurrentSceneName())
            if scene and scene.view then
                display.save(scene.view, display.pixelWidth .. 'x' .. display.pixelHeight .. '_' .. math.floor(system.getTimer()) .. '.png')
                return true
            end
        end
    end)
end

It uses my app.lua

app.isSimulator - just to make sure it doesn't run on devices.

It uses storyboard, you might want to convert it to composer.

Screenshots are saved into the Documents directory.