lockable chain link
I was looking into handcuffs and bypasses and stuff and I stumbled across the Eisenjörg lockable chain link
http://www.andys-handschellensammlung.de/main/others/eisenjoerg/Eisenjoerg.jpg
A bit mroe info from the site I found them at:
http://www.andys-handschellensammlung.de/main/others/eisenjoerg/eisenjoerg_en.htm
=== WARNING DANGER OF TYPOS!===
Arfspeak: calnin cladycomes: you allow her key in themodning
Equals in plain English: cleaning lady comes: you allow her key in the morning