Which channel is not commonly used for alarm transmission to an OPR?

Ultrasonic pulses are not commonly used for alarm transmission to an operations response center (OPR). While the other options represent well-established methods for transmitting alarm signals, ultrasonic pulses are primarily associated with proximity sensors and certain types of motion detection technologies, rather than for alarm communication.

Wired telephone lines, IP connections, and cellular networks are considered reliable and widely used channels for transmitting alarm signals. Wired telephone lines have been a traditional method for years, while IP connections and cellular networks have gained popularity due to their versatility, reliability, and ability to support remote monitoring.

Understanding the distinctions among these transmission methods highlights why ultrasonic pulses are not utilized for this purpose, as they do not facilitate direct communication for transmitting alarm signals to an OPR.