An intrusion detection and prevention system component that monitors and analyzes network activity and may also perform prevention actions.
Source(s):
NIST SP 800-150 from NIST SP 800-94

  A device that produces a voltage or current output that is representative of some physical property being measured (e.g., speed, temperature, flow).
Source(s):
NIST SP 800-82 Rev. 2 from The Automation, Systems, and Instrumentation Dictionary

  A device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. A sensor is a device, which responds to an input quantity by generating a functionally related output usually in the form of an electrical or optical signal.
Source(s):
NIST SP 800-82 Rev. 2

  A portion of an IoT device capable of providing an observation of an aspect of the physical world in the form of measurement data.
Source(s):
NISTIR 8259 from NISTIR 8228