Shield

The Shield (a.k.a Normal Shield, Barrier Shield or just Barrier) is a classic power-up item, first introduced in Sonic the Hedgehog. It is obtained by destroying an Item Box with a blue circular symbol on the monitor. It is the first and original of all shield type power-ups.

The power-up itself envelops the playing character in a spherical barrier which protects the wearer from attacks or damage so that the player would not loose collected rings or a life if they are hit without rings. Its color varies from blue, green and grey depending on what game it is in. Unlike its successors, it does not have any additional abilities to grant to the wearer.

This shield returns, along with the Elemental Shields (Fire, Thunder and Water), in Sonic Generations. However, you'll have to buy this shield and the others via ths Skill Shop. In the 3DS version, it can be found on Item Boxes, as well as the Thunder shield (Emerald Coast only) or get either of them as an extra skill after playing Versus Mode online.

Adventures of Sonic the Hedgehog
In the episode "Robotnik's Pyramid Scheme" the Mummified Hedgehog gave Sonic a necklace that creates a Blue Shield, protecting him from Robotnik's immortality.