A device invented by Genevieve Lefoux as a child. Also called an "anti-mechanical mobility and magnetic disruption emission switch." When activated, the device shuts down other mechanical devices for 6 seconds. A later, more developed version of this is seen in the special parasol Madame Lefoux designs for Alexia.
The device can be strapped to the wrist, and looks like a small brass jewelry case attached to a wide leather band, covered in dials, wheels, and small knobs.