Code From: Tutorial: Continuous Actions in Corona http://coronalabs.com/blog/2014/02/04/tutorial-continuous-actions-in-corona/

fireLasers.lua

local function fireLasers()
    local blaster = display.newImageRect("laserbeam.png", 8,24)
    blaster.x = ship.x
    blaster.y = ship.y
    transition.to(blaster, {time=1000, y = 0 })
end

local needToFire = false

local function handleEnterFrame( event )
   if ( needToFire == true ) then
      fireLasers()
   end
end
Runtime:addEventListener( "enterFrame", handleEnterFrame )

local fireButton = display.newImageRect( "firebutton.png", 64, 64 )
fireButton.x = 50
fireButton.y = display.contentHeight-50

local function handleFireButton( event )
   if ( event.phase == "began" ) then
      -- fire the weapon
      needToFire = true
   elseif ( event.phase == "ended" and needToFire == true ) then
      -- stop the weapon
      needToFire = false
   end
   return true
end

local fireButton = widget.newButton{
   width = 64,
   height = 64,
   defaultFile = "firebutton.png",
   overFile = "firebuttonDown.png",
   onEvent = handleFireButton
}
fireButton.x = 50
fireButton.y = display.contentHeight-50

local function onKeyEvent( event )
   if ( event.keyName == "buttonX" ) then
      if ( event.phase == "down" ) then
         needToFire = true
      else
         needToFire = false
      end
      return true
   end
   return false
end
Runtime:addEventListener( "key", onKeyEvent )