Described techniques enable thwart detection for warning lights associated with recording devices, such as cameras. A warning light may be used to alert bystanders that a recording is in progress, but an operator of a recording device may attempt to circumvent the warning light by obstructing the warning light. A lightpipe or other light guiding element may be used to guide a redirection of the warning light to a light sensor. Then, when the redirection exceeds a threshold, which may be determined based in part on a baseline level of ambient light, recording operations of the recording device may be automatically deactivated.