1. A control device, connected via a communication network to a server device that offers a service, detecting a state of an object to be monitored, wherein the control device performs an operation according to a detected state of the object in accordance with a parameter determining an operation of the control device which operation corresponds to the detected state, and the control device modifies the parameter in accordance with a parameter modification command which is received from the server device via the communication network, wherein the parameter modification command is a command, from a user of a communication terminal device connected to the server device via the communication network, for modifying the parameter.