The Remember Ring.

Never forget anniversaries anymore with the Remember Ring. This ring uses a "hot spot" technology that warms up to 120° F for 10 seconds, every hour on the hour, beginning 24 hours before the special day:

Hot enough to cause discomfort but not hot enough to burn-the Remember Ring™ is impossible to ignore!

Apparently, some men need multiple rings for multiple "special days":

Some fans of the Remember Ring™ wear multiple rings. "I got two of ‘em." says Jon Harshmen, "Well, I got one actually-my wife got me the other one." Holding up his hands to show both rings he says, "Anniversary and Birthday, baby. It’s like a hand gun. Better to have it and not need it, than need it and not have it."

Link - via Gizmodo