Devices, methods, and systems for detecting faults on a spur wired alarm circuit are described herein. One system includes a bipolar capacitor coupled to a last device on a spur wired alarm circuit, a voltage supply coupled to the spur wired alarm circuit, and a controller configured to operate the voltage supply such that a current flows through the spur wired alarm circuit, operate the voltage supply such that the current stops flowing through the spur wired alarm circuit for a particular amount of time, determine a voltage across the bipolar capacitor while the current has stopped flowing through the spur wired alarm circuit, and determine whether a fault has occurred on the spur wired alarm circuit based on the determined voltage.