A portable radar interferomter was used to periodically monitor a rock wall, where millimeter‐scale displacements (0.5‐0.6 mm/month) on an unstable rock slab were detected. Preliminary interpretation of a radar images acquired over a 5 month period revealed evidence for combined toppling and buckling failure mechanisms on the rock slab. The rock wall of interest has a history of block fall activity, which directly endangers a roadway in Canton Graubünden, Switzerland.