When in place around the wrists they slightly weaken the one shackled, more so the more they struggle, and are sealed magically so they can not be opened save by the one who closed them, or by a very powerful mystic locksmith. They look like this save the chains are longer, and they have rigging at the base so that they can be shortened temporarily. 

[img]http://thumbs1.ebaystatic.com/d/l225/m/mxdvVSvYTvodBLhMq-p8m4w.jpg[/img]

Alexi will have to put them on Erik himself and the flat pads will draw a bit of his blood when he seals it.