Create a sprite that is just a horizontal line.
Spawn the line from the "source" object
Then set its width to the distance between both objects e.g. distance(source.x, source.y, dest.x, dest.y)
Then set its angle of source object towards the "dest" object
You can see a tutorial for a lazer with the affect here:
scirra.com
/tutorials/588/how-to-make-a-laser-for-tds
For "untouch" just destroy the line object.