According to a first aspect of the invention, there is provided a monitoring and security arrangement for electrical equipment including an electrical socket device and a control unit, the socket device including a detection means for detecting whether an electrical plug is connected therewith and communication means responsive to the detection means for communicating to the control unit the result of any detection operation performed by the detection means, and the control unit including a receiving means responsive to the communication means.

The arrangement may include at least one repeater device for amplifying a signal communicated to the control unit.

According to a second aspect of the invention there is provided an electrical socket device for an electrical equipment monitoring and security

arrangement, which includes a detection means for detecting whether an electrical plug is connected therewith and communication means responsive to the detection means for communicating to an associated control unit the result of any detection operation performed by the detecting means.

According to a third aspect of the invention there is provided a control unit for an electrical equipment monitoring and security arrangement, which includes a receiving means for receiving a detection signal from a plurality of associated socket devices.

Preferably, the detection means is in the form of an activator switch.

The socket device is preferably adapted to mate with a conventional mains power supply outlet and includes socket formations for mating with the prongs of a power plug.

The activator switch may include a microswitch and a movable shield member located near, and shielding the mouth of one of the socket formations when no prong is inserted in the socket formation, the shield member being adapted to be displaced from the socket formation when a prong of a power plug is inserted into the socket formation, displacement of the shield member operating the microswitch, in use.

In one form of the invention, the socket device includes a microprocessor and a modem for transmitting and receiving a communication signal to and from the control unit.

The socket device may include an isolator switch for electrically isolating the socket formations thereof from the power supply outlet.

In a preferred form of the invention, the security arrangement includes a plurality of socket devices as described above.

Each socket device preferably includes an identification code.

The identification code may be programmed into the socket device's microprocessor or associated memory.

The control unit may include a microprocessor and a modem for transmitting and receiving communication signals to and from the socket devices.

The control unit may further include polling means for polling one or more socket devices, the polling means transmitting, in use, an identification code of a particular socket device to all the socket devices forming part of the arrangement and

waiting for a response from the socket device whose identification code corresponds with the transmitted code.

The socket device preferably includes a polling response means adapted to recognise its identification code when it is received from the control unit and to transmit a polling response signal back to the control unit.

The polling response signal is preferably the socket device's identification code.

The control unit preferably polls the socket device or units continuously.

In a preferred form of the invention, the control unit's microprocessor includes a database for storing the identification codes and equipment data relating to the socket devices forming part of the arrangement. The database may be stored in non-volatile memory.

The equipment data may include details of the electrical equipment with which each socket device is associated.

The control unit may furthermore include an alarm device.

The alarm device may provide an audible or visual alarm or a combination thereof.

The control unit's microprocessor is preferably adapted to activate the alarm device when no response signal is received from a polled socket device.

The control unit may furthermore include a visual display means for displaying the identification code and equipment data of each socket device.

In a preferred form of the invention, the display means displays the identification code and equipment data of a polled socket device which failed to transmit a polling response signal The control unit may furthermore include a keypad for entering identification codes and equipment data into the control unit's database.

In one form of the invention, the isolator switch may be activated and de- activated from the control unit.

The communication signals between the control unit and the socket device may be transmitted via mains electrical conductors.

One embodiment of a monitoring and security arrangement in accordance with the invention is now described, by way of example, in more detail with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of a first embodiment of a control unit according to the invention; Figure 2 is a diagrammatic representation of a first embodiment of a socket device according to the invention; Figure 3 shows how the control unit and a number of socket devices are connected in an electrical power reticulation system; Figure 4 is a flow diagram illustrating the operation of the monitoring and security arrangement; Figure 5 is a circuit diagram of a second embodiment of a control unit having some of the features shown in Figure 1; and Figure 6 is a circuit diagram of a second embodiment of a socket device having some of the features shown in Figure 2.

Referring now in particular to Figures 1 and 2, first embodiments of a control unit 10 and a socket device 12 of a monitoring and security arrangement according to the invention are shown therein.

The control unit 10 includes a microprocessor 14 connected to a modem

16 via an isolator 18.

The control unit 10 further includes a keypad 20, an LED indicator 22, an alarm buzzer 24, and an LCD display 26. The microprocessor 14 controls a relay 30 to activate an external alarm (not shown). An interface device 28 is provided to connect the control unit 10 with an external computer (not shown). The control unit 10 is powered by a 5 volt power supply 32. The control unit further has a non-volatile memory module 33.

The socket device 12 also includes a microprocessor 34 which is connected to a modem 36. The socket device has an activator switch 38 which is connected to the microprocessor 34 and supplies the microprocessor 34 with an input signal. The socket device 12 has a solid state isolating switch 40 which is controlled by the microprocessor 34 to isolate any electrical equipment connected to the socket device 12. A code module 43 is provided, whereby a unique identifying identification number is designated for each socket device 12 in the arrangement. The socket device 12 also has a 5 volt power supply 42 for supplying power to the microprocessor 34, the modem 36 and the switch 40.

Referring to Figure 3, the manner in which the control unit 10 and a plurality of socket devices 12.1 to 12. n are connected to an electricity reticulation

system and electrical equipment is shown. In the drawing, it will be seen that the monitoring and security arrangement comprises a control unit 10 and socket devices 12.1 to 12n. In this drawing, two socket devices, 12.1 and 12.3 are associated with electrical equipment, namely a television set 50 and refrigerator 52 respectively.

Control unit 10 includes a keypad 20, an LCD display 26 and an LED alarm indicator 22. The unit 10 draws alternating current from a mains power supply 54. Conventional mains sockets 56 are connected to the power supply conductors 54 as shown.

The socket devices 12 according to the invention are connected to the conventional sockets 56.

In use, communication signals are transmitted between the control unit 10 and the socket devices 12, via the mains power supply 54, as will be explained hereunder.

A repeater device 11 is connected to socket devices 12.3 to 12.6. A plurality of repeater devices 11, which are all connected to the control unit 10, may be necessary where a large number of sockets 56 are to be monitored and reliable communication is limited by noise and other adverse transmission factors.

In Figure 4, operation of the monitoring and security arrangement is illustrated by way of a flow diagram.

In use, an operator activates a start sequence 42 from the control unit 10. If it is the first time (43) the start sequence is activated, the memory 33 (see Figure 1) is cleared to reset a database (at 44) and the operator enters equipment details and the identification numbers of socket devices used with control unit 10 and repeater 11 into the memory 33 to create the database. The database can be edited at any convenient time.

The microprocessor 14 runs a check sequence on database 46. The check sequence checks for an"end"and sets an"end"if there is none and sets any missing parameters at 46.1.

If the database is full, one entry is moved (at 46.2).

The control unit microprocessor 14 then starts to poll the socket devices 12 connected to the power supply conductors 50 in groups of 500 (at 48).

During the polling sequence, the identification number of each socket device 12 included in the arrangement is transmitted by the control unit to all the

socket devices. Every socket device 12 not transmitting a polling response signal (48.8) is"flagged"48. 5 and the database is checked to determine whether the particular socket is associated with any electrical equipment. If the socket is not associated with any electrical equipment the socket device is"unflagged"48. 6. If it is associated with any such equipment, the microprocessor activates the audible and visual alarms and"flags"the database 48.5. At the end of the sequence 48.1, it is reset 48.2. Similarly, if any key is pressed 48.3 during the polling sequence, it is reset 48.4. Otherwise, the next unit is polled 48.7. An operator can then check which equipment is missing, the location of the socket device in question and take the necessary action.

After the first 500 socket devices have been polled, the next 500 (if applicable) are polled (at 48.9). The microprocessor loads a new start number for polling (at 48.10) and the sequence continues from that number. If at any time a key is pressed on the keypad, the sequence returns to the first step (at 48.11).

The steps as outlined above are repeated until the control unit has polled a maximum of 1 000 000 socket devices, at which time the polling sequence is reset to zero (at 48.12).

A circuit diagram of an embodiment of a control unit 10 in accordance

with the invention is shown in Figure 5. This embodiment has a microprocessor 52, a mains modem 54, a keypad 56, an alarm LED 58, an alarm buzzer 60, an RS-232 connector 62, a 5v power supply 64, and a non-volatile memory module 66.

A circuit diagram of an embodiment of a socket device 12 is shown in Figure 6. As shown, the socket device 12 has a microprocessor 68, a modem, indicated by reference numerals 70 and 80, and an activator switch 72 which is operated by a shutter 74. Further, as shown, the socket device 12 has power input terminals 76 which are connected to the pins (not shown) and power output terminals 78 which are connected to the socket formations (not shown). A coding module, having a non volatile memory, by means of which the identification number of each socket device 12 is designated form part of the microprocessor 68.