I have a solution for the problem of a pilot getting locked out of the cockpit allowing the co-pilot to commit suicide taking 149 other innocent people with him. Doesn't require expensive hardware, only a policy change. Make the cockpit a "No Lone Zone". Military folks will recognize this as an area designated for the buddy system. In other words you are never allowed to be alone in the aircraft cockpit. When either the pilot or co-pilot wants to leave, another member of the crew must take his place.
