In this paper, we propose a method to detect an unauthorized control signal being sent to a remote-controlled system (deemed an ldquointrusion faultrdquo or ldquointrusionrdquo) despite attempts to conceal the intrusion. We propose adding a random perturbation to the control signal and using signal detection techniques to determine the presence of that signal in observations of the system. Detection of these perturbations indicates that an authorized or ldquotrustedrdquo operator is in control of the system. We analyze a worst case scenario (in terms of detection of the intrusion), discuss construction of signal detectors, and demonstrate our method through a simple example of a point robot with dynamics.