NUT is Network UPS Tools. One machine talks to the UPS over USB and publishes status so other machines can shut down too. The USB host is the primary. Everyone else is a network client that listens for "on battery" and "low battery," then runs its own shutdown timer. The picture is a single smoke alarm with extra bells on every floor: one sensor, many rooms that need the warning.

How it works

One USB cable still does the sensing. A HID-compliant UPS plugs into a NAS or a Linux box. That host runs the NUT server (or the Synology/QNAP "Network UPS Server" checkbox, which is the same idea). Clients install NUT upsmon (or the vendor equivalent) and point at that host. Keep the primary scheduled to stay up longer than the secondaries, or the clients lose their signal mid-shutdown.

You do not need a second USB dongle per PC. You need the server IP allowed on the NAS, and a timed shutdown (often 5 to 10 minutes) rather than "run until the battery dies" if the UPS is shared.

When it matters

It matters as soon as two computers share one UPS. A Synology or QNAP that is the only load can shut down from USB alone. Add a desktop, a second NAS, or a home-server PC, and USB cannot reach them all. NUT is the LAN path.

Skip NUT if the UPS only protects one device and that device already speaks HID USB.

These are the HID USB UPS units from the auto-shutdown guide. Pure sine is the path of least resistance for NAS power supplies.

The CyberPower CP1500PFCLCD is the usual NAS-plus-network pick: 1500VA/1000W, pure sine, HID USB. View on Amazon when one UPS must cover the NAS and still have room to share.

The CyberPower CP850PFCLCD is the smaller 850VA/510W sibling with the same USB workflow.

The APC Back-UPS Pro BX1500M stays common in mixed offices. USB shutdown works on many Synology setups; the waveform is simulated sine, so watch active-PFC quirks.

For the DSM and QTS USB clicks, then the NUT-style network share, read How to Set Up UPS Auto-Shutdown on a Synology or QNAP NAS.