Keyless entry systems are already very common in offices. The newest use RFID tags. RFID Digital Locks are also available for homes. The Gadget Home has the MyKey 2300 on their site.
The RFID tag to open the lock can be for instance placed inside a mobile phone (see photo below).
The MyKey 2300 also has a pin number input. Besides that this digital lock also looks quite good. I have no information yet on the price.
More details on the MyKey datasheet.
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