Volrath's Motion Sensor is a uncommon Enchantment — Aura card from Unglued (UGL), collector number 39. Current market price: $0.44, TCGplayer market prices via Scryfall.
Enchant player As this Aura enters, choose one of enchanted player's hands. That player balances this Aura on the back of that hand. When this Aura falls off the chosen hand, sacrifice this Aura and enchanted player loses 3 life.