A Polarity Device is a small device that reverses the controls on Downer Detectors, Headmistresses and Spankers.
Function
The player, having a polarity device in their inventory, has to find a control box. By opening it, they have the option to disable it completely with a Shortspike, or use the Polarity Device.
Using the polarity device will effectively reverse the device the control box connects to, as in, Downer Detectors will now detect Wellies, effectively confusing them for Downers, and attack them instead, allowing the player to go right past without getting detected.
The effects of a polarity device only last for 20 seconds before reverting back to its usual functions.