Laser levels have become common place, but now there is a new one. This little pyramid projects a vertical laser line on the wall and automatically levels itself even if the floor is slightly out of level. This is great if you want to line up window or door frames, hang wallpaper or set tiles. You can't cover up your vertical line! Put it on the floor and it will give you a straight line on the floor and up the wall as well, if you want to line up patterns, or lay floor tiles.
I love it and it was selling for under $100 as the Laser Vision Plumb Pyramid from Zircon -- but I must now preciously guard it from all borrowers because they took it off the market. I just hate it when my favorite toys disappear to the Gods of mass marketing. Some similar but more expensive vertical level lasers have appeared in the flood of laser products now on the market. Check their self-leveling capacity against a good old plumb bob cord before trusting one. You can do that right in the store. (Oh store clerks hate me when I say things like that on national TV.)