That one's not loading for me, but I found this large image: http://i819.photobucket.com/albums/zz117/NewYorkCompany1/Ele...

Yes, the the picture shows why it's allowed in prisons: it's transparent so the guards can see that there's nothing hidden in it.

THANK YOU! Even the wikipedia page didn't have one.

also alt url > http://museum.vaesite.net/__data/edeeddf9608c270fa23148b275a...