LaserBall

A spherical rotating laser that projects level or plumb lines on walls, floors, and ceilings.
No bigger than a tennis ball, it's so easy to use even a novice will experience instant success.
Just attach the mounting cup to almost any flat surface with the included non-marring self-adhesive discs. Then place LaserBall in the cup, turn it on, and watch the internal LED glow a cool blue to indicate that the unit is on.
Rotate the ball to project either a horizontal or vertical line, as desired, and adjust the ball in its mounting cup to determine the length of the line.
Pointing the laser toward the wall will result in a shorter, brighter line, while angling it further away will lengthen the line.
With a final check of the bubble level at LaserBall's center, users can be sure lines are level or plumb.