Yep, that's the Surface Book (original). I've got one, and mine still works! Somehow.
That detach mechanism is insane. As far as I've been able to put together (I haven't done a patent search or anything, just heard bits from people who'd know), there's no motor involved... it's way weirder. I believe the thing actually heats up a nitinol shape-memory alloy latch in the base so it detaches from the tablet piece. That heating is why it takes a couple seconds. But then reattachment is instant, so it's just something clicking in to place. And you can't reattach immediately, because the base has to cool down (just a few seconds, short enough that you never notice unless you're deliberately messing with it). Black magic!
I'm not 100% sure of any of the above, except the use of nitinol somewhere. That's right, the weirdest piece of the conjecture is the only one I've got hard confirmation of. Like I said, black magic.