SmartKeys was developed by Siemens in the mid-1990s and introduced by Mercedes-Benz in 1997 to replace the infrared security system introduced in 1989. Daimler-Benz filed the first patents for SmartKey on February 28, 1997 in German patent offices, with multifunction switchblade key variants following on May 17, 1997. The device entailed a plastic key to be used in place of the traditional metal key. Electronics that control locking systems and the ignitions made it possible to replace the traditional key with a sophisticated computerized "Key". It is considered a step up from remote keyless entry. The SmartKey adopts the remote control buttons from keyless entry, and incorporates them into the SmartKey fob.
Once inside a Mercedes-Benz vehicle, the SmartKey fob, unlike keyless entry fobs, is placed in the ignition slot where a starter computer verifies the rolling code. Verified in milliseconds, it can then be turned as a traditional key to start the engine. The device was designed with cooperation of Siemens Automotive and Huf exclusively for Mercedes-Benz, but many luxury manufacturers have implemented similar technology based on the same idea. In addition to the SmartKey, Mercedes-Benz now integrates as an option Keyless Go; this feature allows the driver to keep the SmartKey in their pocket, yet giving them the ability to open the doors, trunk as well as starting the car without ever removing it from their pocket.
The SmartKey's electronics are embedded in a hollow, triangular piece of plastic, wide at the top, narrow at the bottom, squared-off at the tip with a half-inch-long insert piece. The side of the SmartKey also hides a traditional Mercedes-Benz key that can be pulled out from a release at top. The metal key is used for valet purposes such as locking the glovebox and/or trunk before the SmartKey is turned over to a parking attendant. Once locked manually, the trunk cannot be opened with the SmartKey or interior buttons. The key fob utilizes a radio-frequency transponder to communicate with the door locks, but it uses infrared to communicate with the engine immobilizer system. Original SmartKeys had a limited frequency and could have only been used in line-of-sight for safety purposes. The driver can also point the smart key at the front driver side door while pushing and holding the unlock button on the SmartKey and the windows and the sunroof will open in order to ventilate the cabin. Similarly, if the same procedure is completed while holding the lock button, the windows and sunroof will close. In cars equipped with the Active Ventilated Seats, the summer opening feature will activate the seat ventilation in addition to opening the windows and sunroof.
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