A clamp mechanism for securing an in-ceiling surveillance camera housing assembly to a ceiling. The clamping mechanism advantageously allows easy installation of the camera housing in the ceiling via a camera housing aperture without requiring a large access aperture adjacent the camera housing aperture. The clamping mechanism also allows easy removal of the housing if, for some reason, the housing must be removed because the clamping mechanism is bidirectional and may be stowed within a groove on an outer surface of the housing. Once the clamping mechanism lowers a clamp to secure the housing assembly to the ceiling, a window and trim ring assembly is locked to the housing assembly to discourage removal of the window and trim ring assembly and prevent access to the clamping mechanism.