From The Heretic Knowledge Vault
Magical gadgets applied to captives (like, say, Sara Amraphel) to restrain them from doing harm to themselves, or particularly, others. Sarine keeps a set in her bag of tricks and applies them here. Jon doesn't think very highly of them, and uses his opinion to open a friendly chat with his sis -- staking out the intellectual high ground, as usual when a big brother counsels a little sister.
We don't know where they came from, but presumably the Kiyan Nizami affair convinced the elves that they'd be useful to have around. According to Sarine, they include a complicated, enchanted lock system plus "a few other little tricks" that we haven't seen yet.