Davis Self-Inflating Key Bouy 
The ultimate key fob for boaters! When keys fall in the water, Key Buoy self-inflating key ring opens up, releasing an air tube which inflates automatically. The 14" (47 cm) inflated tube extends above the water, allowing you to reach over and pick them up. Key Buoy rises to surface in as fast as 60 seconds. May take longer in deeper water with maximum weight attached.
Strong enough for items weighing up to 2.8 ounces (80 grams) such as keys, small tools, deck plate keys. Suitable for single use only, so keep a spare on hand!
Quick Guide (pdf)