Abstract: A corner-mounted shield for protecting monitoring devices includes a triangular protective plate attached to three adjacent corner-forming interior room surfaces (e.g. two walls and ceiling). Attachments to the corner-forming interior room surfaces are made behind the protective plate, usually through an opening in the protective plate, and are inaccessible after the opening is covered by a window. The window is attached to the protective plate with tamper-resistant fasteners and is essentially transparent to whatever is being monitored by the monitoring device. The monitoring device, mounted behind the protective plate and window, has a clear view of the monitored room through the window because the protective plate faces into and is within the monitored room.