The Simmons Family Ring (シモンズ家の指輪 Shimonzu-ka no yubiwa ) is a key item in Resident Evil 6.
In Leon's campaign this ring is needed to go through the catacomb gates to the flooded area. After using the ring the gates won't open permanently but a wave of Zombies and Bloodshots will appear.
This ring is found by Ada Wong while exploring the underground forest cemetery area in/near Tall Oaks. It is inside of a chest that is only accessible after completing a puzzle. The puzzle involves three zombies and a floor that gives way when too much weight is applied. If Ada attempts to jump the gap onto the area where the chest is, the floor will open up and drop Ada below and she will have to make her way back up.
To obtain the key, Ada must use her Crossbow to pin the zombies to the far wall. Doing this will allow Ada to safely walk on the floor and obtain the item. This ring will open a door necessary to move deeper into the catacombs.
She gives the ring to Leon during their paths crosses in catacombs. Leon uses this item in Chapter 3 of his campaign.