I built something similar too: https://vine.co/v/hmu5IlBj2pQ https://vine.co/v/hmu5IlBj2pQ Mine uses NFC keys. Arduino does a lookup over GPRS against a web s

I built something similar too: https://vine.co/v/hmu5IlBj2pQ https://vine.co/v/hmu5IlBj2pQ Mine uses NFC keys. Arduino does a lookup over GPRS against a web service to check if the key is permitted to unlock. As someone else has commented, this uses an electric door strike rather than a servo. You can register new keys using the webapp, make them allowed for certain time periods etc.