# Interlock

> The interlock banner of a unit panel, its states, the manual rearm and its permission.

The **Interlock** banner shows the live stop-interlock status of a unit and offers the
manual rearm (see [Automation](process-automation) for what a stop interlock is and how it
ends runs). It is a part of the [unit panel](view-unit-panels), not a component: the panel
draws it above its cards, for its own unit, while the unit's model has its stop interlock
enabled. It is never placed on a screen, and the dashboard's Add palette does not offer it,
so there is nothing to configure.

## What it shows {#what-it-shows}

A healthy interlock is deliberately silent: in the **Normal** state the banner draws
nothing and takes no room on the panel, so it claims the operator's attention only when
something needs it.

| State | How it is drawn |
|---|---|
| Normal | Nothing. The banner collapses. |
| Interlock tripped | A loud critical banner: a live external stop is in force and runs end. |
| Interlock awaiting reset | A caution banner with the **Rearm** button. |
| Interlock unavailable | A caution banner reporting that the status cannot be read (no source configured, or the Process service unavailable). |

Every banner carries the state's reason line plus the configured source's name, its
current Boolean value (`True`, `False`, or the gap mark when it has none) and its quality
(`Good` or `Unavailable`). The transient result of a rearm is written on the banner too.

## Rearming {#rearming}

**Rearm** appears only in the awaiting-reset state. It is enabled while all of these
hold:

- the physical source has cleared (the latest status says a rearm is safe),
- the unit is not busy with a run,
- no rearm call is already in flight.

While one of them does not hold, the button stays drawn, greyed.

The rearm is journaled with the name of the signed-in operator (or `Not signed in`), and
the permission is rechecked at the moment of the press, never only when the panel was
drawn.

## Permission {#permission}

Rearming takes the **Run procedures** permission, on the Process page and on the View page
alike. A role without it still reads the whole banner, but the Rearm button is not drawn for it:
that role can never rearm.