[@silvermist1116] So, your new power may need a little explaining. Mostly because I don't get what she does with the 'matter' she's absorbed. Does she become an object made of said matter? A golem? Does she just absorb matter like a sponge and voila? You need to be a lot more precise here, because matter is literally anything you can touch in the world, so no energy or soundwaves or nothing. But that's still absurdly open ended, so I'm simply asking for extra details. 

[@Keksalot] Good thing a collar can be opened and closed o; o; o;

Also easy, the device can simply restrain the specific means their bodies employ to exert the powers. 

Sure they could have tailor-made stuff, but for your character for instance, you'll get 0 character interaction until the escape if that's the case' A collar just makes it convenient and easier for everyone to be in the same room without a couple powergaming the shit out of my patience. 

When locked up they can have extra secure cells tailor made, however.