An electrical relay is a:

An electrical relay functions as a remotely controlled switching device. It operates by using an electromagnetic coil to open or close contacts within an electrical circuit. When a small current flows through the coil, it creates a magnetic field that either allows or interrupts the flow of a larger current in another part of the circuit. This capability makes relays particularly useful for controlling high voltage or high current devices with a low voltage signal, enabling remote or automated control of various applications such as in automation systems, home appliances, and industrial controls.

In contrast, the other options describe different functions: a resistance-based circuit focuses on the relationship between voltage and current without involving remote control, a signal amplifier is used to increase the strength of a signal, and a voltage regulator maintains a constant output voltage regardless of variations in input voltage or load conditions. Each of these options serves distinct purposes, reinforcing the unique role of a relay in electrical systems.