
Determine the topic of the question-answer pair.
Question: "what cars have smart key systems?";  Answer: "It was first developed by Siemens in the mid-1990s and introduced by Mercedes-Benz under the name "Keyless Go" in 1998 on the W220 S-Class following its design patent filed by Daimler-Benz on May 17, 1997."? Topic: 