1,079,931. Monitoring apparatus. EDWARDS CO. Inc. Oct. 9, 1964, No. 41322/64. Heading H4K. [Also in Division G4] Apparatus for monitoring the operating condition of equipment at a remote location comprises a number of two-state devices, e.g. switches 94c to 94k, Fig. 1, which by their state indicate the operating condition of the equipment to be monitored, and a rotary switching device, e.g. drum 18, whose rotation is initiated by the reception of a signal over a communication system to cause the two state devices, e.g. switches 94c to 94k, to be connected, in coded sequence, in series with a signalling device, e.g. bell 79, whose signals are transmitted over the communication system to the monitoring station. The apparatus as described is monitored over the public telephone line L1, L2 the operation of the device being initiated by the reception of the ringing signal which operates relay 14 to supply power to motor 28, to start rotation of the switching drum 18, and also operates relay 38 which self holds over contacts 46 and so maintains the motor supply over contacts 40 so that breaks in the ringing current do not stop the rotation of motor 28. Cam wire 31 on the drum maintains this condition for a short while to allow the telephone bell to ring and a local operative to answer the call if present, otherwise, at the end of the predetermined time, switch arm 24a changes over and breaks with contact 30, deenergizing relay 38, but makes with contact 48 and operates relay 52 which completes the telephone line circuit over contacts 58 and 60 and maintains the motor drive over contacts 54. Further rotation of the drum then operates switches 24b to 24k in a code sequence. Preferably switch 24b operates repetitively to sound the buzzer 74 and between each operation of the buzzer 74 one of switches 24c to 24k is operated to connect the respective switch 94c to 94k in series with the power supply to bell 79. If the selected switch is closed, e.g. due to a fault in the corresponding part of the apparatus being monitored, the bell rings and it is arranged, by inserting a number of pegs in the surface of the drum, that the bell rings a number of times characteristic of the particular switch that is closed. The sounds of the bell and the buzzer are transmitted to the monitoring station by microphone 12 over lines L1 and L2. After one complete revolution of the drum, bar 31 operates switch 24a and relay 52 is released so de-energizing the motor 28 and releasing the line connection at contacts 58 and 60. If an operative at the remote station wishes to interrupt the monitoring sequence and communicate with the main staton he presses a button 104 which operates relay 82 which self holds over contacts 78 and, via contacts 80, interrupts the power supply to the drum switches 24b to 24k. The drum therefore completes its cycle of operation but the bell and buzzer are prevented from sounding. The embodiment of Fig. 1 provides 9 monitoring switches, but this number can be doubled by a modification of the arrangement as shown in Fig. 5 in which each switch 24 is associated with two monitoring switches 94 one connected in circuit with the bell 76 and the other with a chime 140. The switch operating pegs are duplicated over each half of the drum surface, the switch 241, operated by bar 136, selecting the bell to operate over one half revolution of the drum and the chime to operate on the other half revolution. The diodes 148 prevent lines 143 and 134 being shorted together when both switches 94 associated with one switch 24 are closed. Also described is a method of coupling two units together so that one drum operates first and then the other drum, Fig. 6 (not shown). Also described are alternatives to the drum, in one of which a circular plate has the contacts printed on it and the contacts are scanned by a wiper brush, Figs. 10 and 11 (not shown), and in the other, beaded belts are driven by a drum having depressions to engage the beads, and hoods are crimped over individual beads to enlarge them to a sufficient diameter to operate switches mounted adjacent the drum, Fig. 9 (not shown).