Is there way to identify if the walls are moving?
The best way is to monitor the alignment voltage. Please do not reset the DS240/241- doing so will recalibrate the beam smokes and will give wrong readings.
Another suggestion is to mount a laser pointer near the beam smoke on the wall. Mark where it hits the other wall leave it for 2 to 3 hours or longer and see if the laser point moves from its original mark.
Part numbers DS240, DS241, D296, D297