Dumbledore’s impossible soul detector - how could he have built this?

in the 5th book, after Harry saw the snake attack Arthur Weasley, Dumbledore uses a strange silver device and asks, “but in essence divided?” we never see this device again, and harry never asks Dumbledore what it actually does.

Dumbledore now swooped down upon one of the fragile silver instruments whose function Harry had never known, carried it over to his desk, sat down facing them again, and tapped it gently with the tip of his wand.

The instrument tinkled into life at once with rhythmic clinking noises. Tiny puffs of pale green smoke issued from the minuscule silver tube at the top. Dumbledore watched the smoke closely, his brow furrowed, and after a few seconds, the tiny puffs became a steady stream of smoke that thickened and coiled in the air... A serpent’s head grew out of the end of it, opening its mouth wide. Harry wondered whether the instrument was confirming his story: He looked eagerly at Dumbledore for a sign that he was right, but Dumbledore did not look up.

“Naturally, naturally,” murmured Dumbledore apparently to himself, still observing the stream of smoke without the slightest sign of surprise. “But in essence divided?”

Harry could make neither head nor tail of this question. The smoke serpent, however, split itself instantly into two snakes, both coiling and undulating in the dark air. With a look of grim satisfaction Dumbledore gave the instrument another gentle tap with his wand: The clinking noise slowed and died, and the smoke serpents grew faint, became a formless haze, and vanished.

how do you think a wizard could even make a device like that in the HP world? we know distance matters in magic (like with apparition limits, spell range, etc), so how could something on Dumbledore’s desk detect from hundreds of miles away that Voldemort isn’t controlling anyone right now? is it tied to legilimency, soul, some kind of magical signature? and when do you think Dumbledore actually built it?