A method of requesting access through a door may involve: causing a mobile computing device to receive an identifier of the door; and causing the mobile computing device to transmit an access request to an access-control system, the access request comprising data representing at least the identifier of the door and an access code. A method of controlling access through a door may involve: receiving an access request from a mobile computing device, the access request comprising data representing at least an identifier of the door and an access code; and in response to the request, allowing access through the door. Systems are also disclosed.