Abstract: In a method of inventorizing a plurality of data carriers (2) with the aid of a communication station (1) communicating in a contact-free way with the data carriers (2), a set (TS(1), TS(2), . . . TS(N), TS(N+1), . . . (TS(K)) of transmission parameters, preferably of time slots (TS) is available, which set comprises a first subset (TS(1) . . . TS(N)) and a second subset (TS(N+1) . . . (TS(K)) wherein inventorizing procedures (MP1, MP2, MP3, . . . ) are performed consecutively and wherein uninventorized data carriers (2) transmit their identification data (ID) to the communication station (1) for the purpose of inventorization only using transmission parameters contained in the first subset and wherein already inventorized data carriers (2) transmit their identification data (ID) to the communication station (1) only using transmission parameters contained in the second subset.

Abstract: A security system having a two way wireless keypad which operates in a particular manner for improved operation. The keypad processes information to effectively reduce communications between the control panel and the keypad. The keypad selectively activates and deactivates a transmitter and receiver arrangement for power conservation reasons. The system provides confirmation of communications between the keypad and the control panel to increase the reliability of the system.