Alerts

Colour in Caliper always means something. A cell is monochrome — tinted by macOS like its own menu bar items — until its reading crosses a threshold you set. There are three states, and only three:

State	Looks like	Means
Nominal	The menu bar’s own colour	Unremarkable. The normal state.
Warning	System orange, dashed underline	Crossed the Warn at threshold
Critical	System red, solid underline	Crossed the Critical at threshold

The underline is there so colour is never the only signal: orange and red are the two hues the commonest colour-vision deficiencies confuse. VoiceOver says it in words — “CPU critical at 95%”.

A cell with no thresholds stays nominal forever. A new cell has none: Caliper does not invent opinions about your hardware. The default Overview widget alerts on CPU at 70% and 90%, and on memory pressure.

Setting thresholds

Select a cell in the editor. Under Alerting:

• Warn at and Critical at — either or both, in the units of the metric being judged.
• Alert on — which metric the thresholds are judged against. Same as displayed metric is the usual choice; None switches alerting off for the cell and clears its thresholds.

Showing one thing, alerting on another

What you watch and what you alert on can be different metrics. Memory is the usual case: a healthy Mac routinely reads 78% used while the kernel reports no pressure at all. Alerting on “used” would cry wolf every day; showing pressure would be a number nobody recognises. So the default memory cell shows how full memory is, and takes its colour from memory pressure.

Any cell can do the same — show GPU load and alert on GPU temperature, or show a disk’s free space and alert on a threshold in bytes rather than percent.

Notifications

Colour in the menu bar is immediate and needs no permission. Notifications are deliberately more reluctant:

• A breach must last 30 seconds before anything is said. CPU crosses 70% dozens of times an hour; an app that notifies on every spike is muted within a day and then never tells you anything again.
• Recovery needs a margin. The reading has to fall meaningfully below the threshold, not merely back under it, so a value sitting right on the line does not flip between alert and recovered.
• No sound. A chime for a CPU spike trains you to ignore chimes.

macOS asks whether Caliper may send notifications the first time one is due. To stop them without touching your thresholds, turn Caliper off in System Settings ▸ Notifications, or set "alertsEnabled": false at the top level of layout.json.

Alerts keep watching while a widget is out of sight — behind a full-screen app, under the notch, or covered by windows. Drawing stops then; judging the thresholds does not.