Using a magnet base, In long hallways you can sometimes attach to the ceiling grid, but if there are light fixtures that hang down, they can interfere with visibility. You might be able to attach to steel door frames, but you should make sure that targets won’t get knocked off if doors get thrown open or slammed closed. You can also attach to glass, either by using steel washers attached to the glass with painters tape, or even using a secondary magnet on the back of the glass such that the glass is sandwiched. I would still add a tape bond, in case there is mechanical equipment in ceilings that might switch on and create vibrations. If you trust the paint quality, you can try using taped washers on the walls, but any dirt/grease (or if the paint is poorly applied) could quickly have or create other problems.
Another option in both hallways and stairwells are traffic cones with targets on top. These are extremely visible, relatively inexpensive, and very fast to set-up. If you have to allow employee access during or between scans, traffic cones in bright safety colors can keep people from tripping over standard tripod legs, and usually take up less floor space. They are available in multiple heights if you want to make sure your targets are on different planes.
Finally, my latest bases have a v-groove and hole that are built in along with the ⅝” survey thread. With a handful of zip-ties, you can very quickly and very solidly attach targets to pipes, conduit or - handrails. And agreed, so many stairwells are identical from top to bottom, so some printed targets which are very clearly numbered to identify the floor or landing can be extremely useful.
I’ve found that just having some spheres is not as important as having target spheres that have been thoughtfully designed and include the accessories necessary so they can be easily mounted or attached and used in the field. Otherwise, a ball is just a ball -
