Can be installed either way over a light switch (over the existing cover) to keep the switch from being turned on, or from being turned off.

When visiting my mother-in-law, she put blue tape over a light switch that controlled an outlet to keep the kids from turning it off. I whipped up this design and printed it out in clear PLA and she asked me to make her a bunch more!

Enjoy!

Just print!
You can use supports if the crosspiece sags, but shouldn't be necessary.