Collar of Silence

A Collar of Silence is a magic item that prevents the wearer from speaking. These collars are carried and used by mage hunter golems. Caleb Widogast was able to modify one of these collars to be powered and used independently of a golem, and it was ultimately permanently fixed to Trent Ikithon's neck with Sovereign Glue.

Description
These collars lock around a creature's neck. They are described as "intrinsically tied" to the mage hunter golems that carry them. They are powered by a central machine tower in the Folding Halls and have no other power source, so are not self-powered. They can be modified to be powered by an arcane battery. They are made of dull, steel-brushed metal and have visible runes in a filigree around the edge. When the collar was independently powered with an arcane battery, its runes glowed the same red as its power source.

The collars used by mage hunter golems automatically activate, but a modified collar needs to be activated with an Arcana check that is higher than 15 but lower than or equal to 24.

A creature wearing an activated collar is unable to speak. The collar as depicted in Campaign 2 possibly prevents specifically verbal components of a spell from being spoken, though no spells with non-verbal components were attempted, and the statblock of a mage hunter golem in Tal'Dorei Campaign Setting Reborn states that no spells can be cast.

The collar can be unlocked with a DC 25 lockpicking check. Its effects may also be dispelled by Dispel Magic.

Campaign 2: The Mighty Nein
While exploring the Folding Halls of Halas to rescue Yussa Errenis, the Mighty Nein encountered a mage hunter golem that guards the Halls. The golem could clamp these collars around the necks of intruders to nullify much of their spellcasting abilities and did so against Caleb. Veth Brenatto picked the lock on the collar to remove it, and Caleb kept it. When the party later found and rescued Yussa Errenis from the prison within the Halls of Halas, he was wearing one of the collars around his neck. Veth was able to remove this one as well.

Caleb found that the collar was rendered inert and determined that he would need an arcane battery, such as that from Aeor, to recharge it. While exploring one of the ruins in Eiselcross, the party encountered such an automaton, and Caleb retrieved the cortex. After much tinkering and his own failures to successfully insert the gem into the collar, he asked Jester to attempt it and she succeeded.

Caleb later gave the collar to Beauregard Lionett, feeling she had a better chance of being able to successfully place it on Trent Ikithon. When Ikithon confronted the party at the Blooming Grove, Veth lined the collar with Sovereign Glue, and Beau placed the collar onto Trent, permanently fixing it to his neck. Astrid, betraying Trent, activated the collar after Caleb's attempt to do so failed.

Campaign 3: Bells Hells
Ludinus Da'leth and the Ruby Vanguard used mage hunter golems to secure the Tishtan excavation site in Marquet while they built a Malleus Key there. Caleb was captured trying to sabotage the Key and was restrained by a golem. Imogen Temult successfully used Command to convince it to release him, but doing so left a Collar of Silence around his neck.