A UPS (Uninterruptible Power Supply) bridges power outages and fluctuations so that connected equipment continues to run without interruption. Depending on the type — offline, line-interactive, or online (double-conversion) — the level of protection varies. In an ISMS, a UPS is a core availability control. It buys you the time needed to shut down systems gracefully or switch to a generator. Battery capacity and UPS health should be tested regularly to ensure reliability when it matters.