This is a Tok'ra Bio Sensor from the fourth season of Stargate SG-1. Items like this were used placed on Colonel O'Neill and his team in order to monitor their physiological state while testing an alien artifact during the episode: Upgrades.
The front of the item is made from both plastic and resin, while the back/inside has three LED lights connected to a small battery. This item has not been tested to light up.
The Tok'ra Bio Sensor measures approximately 1.5" (4cm) in diameter. It is in good production used condition.
COA: Prop Store.