A radio-frequency (RF) signal is a wireless electromagnetic signal in the RF spectrum, typically used for communication, sensing, or interference. In security work, the same physics that carries data can also be used to disturb devices, inject energy, or expose unintended emissions. Because RF travels through air and can couple into cables, circuits, and antennas, it is a common channel in both legitimate wireless systems and attack surface analysis.
RF signals matter in cyber security because hardware does not only fail through software bugs. Attackers may use tuned RF energy to stimulate a device and make hidden behavior easier to measure, or to disrupt normal operation with interference and jamming. Defenders respond with shielding, filtering, careful antenna design, spectrum monitoring, and emissions testing. In practice, RF security is about controlling what a device sends, what it receives, and what it leaks into the surrounding environment.