Abstract: A system for detecting the presence in a compartment of a rack of a portable transmission unit of a number of portable transmission units, each being capable for transmitting or for receiving a signal containing an identification number assigned to the unit. All compartments of the rack or only compartments receiving or having received the units therein are scanned. The presence of a unit in a compartment is acknowledged by the unit after it has received a scanning signal, being identical for each scanned compartment, by providing a response signal comprising the identification number assigned to the unit. For each unit which is present, or until the actual scanning thereof was present, in a compartment a control circuit updates a datum, indicating the presence of the unit in a compartment, in a memory.

Abstract: System for transmitting alarm signals, comprising at least one portable transmitting unit and one central receiver, the transmitting unit comprising a control circuit which is connected to an activation device and a transmitting circuit, the control circuit activating the transmitting circuit when the activation device is energized in order to transmit an alarm signal and in order to re-activate the transmitting circuit for the re-transmission of the alarm signal after the elapse of a delay time, the delay time being different from a delay time of another transmitting unit, the transmitting unit having a memory for storing an identification code allocated to the transmitting unit, the central receiver comprising a processing system which is connected to a receiving circuit which is suitable for receiving an alarm signal and the processing circuit activating a signalling device, on receipt of an alarm signal, for the purpose of generating an attention signal, in which system the delay time is dependent on corr