Lightswitch Guards to block out kids or pesky visitors from turning on/off switches you don't want changed.  Have a completely closed and semi open version.  To flip switch on open version requires a pinch on the switch that is somewhat difficult and deters would be fiddlers.

Additional style of lightswitch blocker is just a plate with an opening will lock the lightswitch in place on or off and is the easiest/fastest print. 

Prints easily without supports.  0.2mm layer height in any material.  

Tried to keep the overhangs to a reasonable angle in the domed cover style.

To install, remove the two screws on the existing lightswitch cover plate and reinstall with the printed piece in place.