A security system comprises a plurality of alarm points distributed at a plurality of positions in a building; signal processing module for receiving alarm signals from at least an alarm point when alarm occurs at the at least an alarm point, transmitting the alarm signals to a server; a database for storing several sets of user information, map data, several sets of alarm point information; the server for receiving user requests from a plurality of clients, responding to the user requests according to the user information, the data map and the alarm point information, and then reverting responses to clients; the clients for sending the user request to the server and receiving and output responses. The present security system is of the advantage that it could be fully computerized and could satisfy the requirements of usage at the same time at several different sites by a plurality of different users.