What is a common feature of control relays?

Control relays are commonly known for their ability to perform specific tasks automatically in response to given inputs without needing manual intervention after initialization. They can be triggered by electrical signals, which enables them to operate based on the parameters set within the system. This automatic functionality distinguishes them from devices that require constant manual input for operation.

While the other features mentioned in the options may be characteristics of certain types of relays or control systems, they do not universally apply to all control relays. For instance, some relays can operate independently, and many incorporate built-in timers or are capable of performing complex operations, particularly when integrated into advanced systems or PLCs. However, the defining attribute of control relays is their ability to function automatically based on an input signal, thus reducing the need for manual control during operation.