The central control unit used by the EASY BY VOICE system is an IBM-compatible PC with Windows NT 4.0. The computer is reserved exclusively for the EASY BY VOICE system and cannot simultaneously be used for other tasks such as word-processing etc. In this way it is guaranteed that there will be no interference with other programmes, which might otherwise affect the system's ability to function or even paralyse it completely.

In other respects, the PC is a standard PC which makes only low demands on the components installed; in particular, no powerful graphics cards or hard disks are necessary. However, the main memory of the computer should be at least 64 MB. Depending on the complexity of the system, the computer also needs one or more passive ISDN cards for connection to the telecommunications system and an NE2000 - compatible 10 Mbit Ethernet network card.

In order to effect a controlled shutdown of the system in the case of a power failure, an emergency power supply is connected to maintain a minimum level of performance. As the system needs no monitor when functioning normally, shorter power cuts of up to half an hour can be bridged without having to shut down the system.

The PC is connected to the house automation system by means of a specially developed Gateway, which is connected to the PC via Ethernet. The TCP/IP protocol is used to communicate with the Gateway. As the PC and the Gateway constitute a local network, i.e. there is no external network connection, there is no danger of interference from outside.

A cordless telephone should be plugged into an analog port of the ISDN box already mentioned. The user picks up the telephone and makes contact to the system by dialling the internal number of the ISDN card located in the computer. The system takes this call and initialises the command structure for the user. This procedure only takes a few seconds. All commands made by the user over the telephone are directed to the system and processed there. When a command is recognised by the system, a reaction occurs immediately, i.e. the relevant switching operation is started. Incidentally, it is not necessary to make a new phone call for every command.

The connection to the system exists until the user places the phone back on the hook. Nevertheless, there is no possibility of commands being carried out in error, because the system has a time-out facility which switches it into "safety mode" after a certain period of time. The system can then only be returned to normal operation by the use of a single word which is not common in normal speech.