A new safety trigger for the Glock has been launched by American Tactical Imports

From the press release

SIDERLOCK® from American Tactical Imports is a security trigger designed for GLOCK® pistols which replaces the original trigger to offer a safer and more secure blockade of the firing action.

The concept is simple; with a push on the safety pin a sliding pin acts to block or release the movement of the central pivot of the trigger whereby avoiding an accidental discharge of the weapon. SIDERLOCK® behaves exactly as the original GLOCK® trigger when it is in the fire position all the while maintaining the original manufacturer specifications and its immediate availability of shot.

Having not seen one I cannot comment on how useful it would be. I just hope no one will draw a Glock in self defense only to have the trigger jam!
American Tactical Imports will be displaying it at SHOT Show this year.