What best describes an alarm shunt?

• A. A fuse that protects the power supply.
• B. A device that triggers the siren on motion.
• C. A sensor that detects tampering.
• D. A relay that holds an alarm switch in the closed state while it is actually open, or in open when actually closed.

Answer: (D)

An alarm shunt is a device that bypasses or falsely changes the perceived state of a sensing circuit. It uses a relay wired in parallel with the alarm switch so it can force the panel to read the switch as closed when the physical contact is open, or open when the contact is closed. This keeps the control panel in a chosen state regardless of the actual condition, effectively “shunting” the real signal. It’s not a fuse that protects power, not a motion sensor that detects movement, and not a tamper sensor; those other devices serve different functions. So the description of a relay that holds the alarm switch in the opposite state best matches an alarm shunt.