Banjo Trigger Capo from Dunlop.
The Dunlop Trigger Capo allows you to quickly and easily change key with a squeeze of the hand. This capo's strong spring-action clamp keeps it firmly in place, while its slim profile ensures that you can play up and down the fingerboard unhindered. Special padding protects your instrument's neck from scratches. Made from lightweight aircraft-grade aluminum, the Trigger Capo is a must on the road when you need to change key on the fly.
Can even be used on the mandolin!