This is a circuit that can be used at night in places like offices, stores, and warehouses, among other places, to determine whether or not the watchman who is responsible for your establishment is working. In order to function, it makes use of an existing telephone that is located as close as possible to the watchman's station (for example, in an office or store). You can send an audible alarm to the watchman by simply dialing the office or store's telephone number from your home or any other location, preferably by using your mobile phone. This should be done as quickly as possible. The provided circuit is able to detect the ring, and the watchman is also provided with a visible warning signal in the form of a bright bulb. Soon after the ring tone, the lamp continues to be "on" for a period of time that is close to sixty seconds. The watchman is given instructions to signify his presence by merely directing the light beam from his torch toward an LDR sensor unit that has been installed on the wall (without lifting the handset off-cradle of the ringing telephone). During the window of time in which the warning lamp is on, this task needs to be completed. In the event that he is unable to complete it within the allotted amount of time, the circuit

will record his absence by increasing a count. If he does it, the count will not be affected in any way. There is room for up to nine distinct alert bells in this scenario. The number that is displayed on the screen is the total amount of times that the watchman overlooked his presence. The timing details can be obtained by using the called number in conjunction with the displayed count on the mobile phone, which records both the called number and the call time. By setting its reset pin 14 to high using the reset switch S1, the telephone lines Counter 74LS192 (IC7) can be reset to the zero state. This applies to both the TIP and RING lines. The IC 74LS47 provides the power for the 7-segment, common-anode display known as DIS1 (IC8). After what feels like an eternity, the count of one is finally displayed as the phone rings. This occurs if the watchman is unable to concentrate the beam of the torchlight on the LDR1. If the LDR1 photoresistor detects light from the watchman's torch within the allotted amount of time, the down clock will remain high until the up clock also reaches its maximum. Since the counter first counts upwards and then counts downwards, the count, in practice, does not change.

Every component, with the exception of LDR1, is stored in a cabinet that is hermetically sealed and has a locking mechanism. Only LDR1 is mounted on the wall and may be seen from the outside. This is done to prevent the counter from having to be reset manually. In the event that the power goes out, the count will not have to be reset because the circuit will be powered by a battery.

1. In the beginning, when the power supply is turned on, the power-on-reset components C8 and R13 reset the counter IC7, and the display shows the number 0. 2. From the outside or from your mobile device, dial the telephone number of the location where the parallel system is installed. In the beginning, the alarm lamp L1 will light up and relay RL1 will become energized. 3. The number "1" is added to the counter whenever the warning bulb L1 is turned off. 4. The counter begins counting up, then counts down, and eventually shows 0 on the display if the watchman focuses the torchlight beam on LDR1 while the alert lamp L1 is still blazing. This provides evidence that the watchman is currently on duty. 5. If the watchman focuses the torchlight beam on LDR1 after the alarm lamp L1 goes off, then up counting will occur, and the display will show the number 1. This suggests that the watchman is not present at the moment.