Many Mercedes vehicles have a keyless entry remote system, which allows you to control your car's locks, boot and alarm with a remote key fob. These key fobs are programmed to match up with your vehicle by the manufacturer, but it is possible to reset many of these Mercedes key fobs in the event of problems with the key fob provided for you.
Place your key in the ignition of your Mercedes vehicle.
Press and hold the "Lock" button down. Continue to hold this button down and remove the key from the ignition.
Press the "Unlock" button five times while still holding down the "Lock" button.
Your key fob is now reset and ready for use.
Modern Mercedes use radio-based key fobs with a highly complex encrypted signal, so this is not foolproof--although it undoubtedly the most reliable method to try initially before going to your dealer.