Specter

A native macOS menu bar app that shows system telemetry at a glance — CPU temperature, per-core breakdown, and fan RPM, with color-coded thresholds and a short history chart.

The app has no Dock icon, no main window, and no chrome. Click the menu bar numeric to see the popover with per-core temps, a 5-minute history chart, and color-threshold settings.

Build

Requires Xcode 15+ and macOS 13+.

One-time setup

This project uses SMCKit via Swift Package Manager. Add it to the project from the Xcode UI:

1. Open Specter.xcodeproj.
2. File → Add Package Dependencies…
3. Paste https://github.com/srimanachanta/SMCKit and click Add Package.
4. Pick the Up to Next Major version rule starting at 1.1.0.
5. When prompted to choose package products, add SMCKit to the Specter target.
6. Build & run (⌘R).

After this one-time step the project is self-contained and rebuilds fine from the command line:

xcodebuild -project Specter.xcodeproj -scheme Specter -configuration Debug build

What you should see

• A numeric CPU temperature in the menu bar, e.g. 65°, colored green / yellow / red by the configured thresholds.
• The app does not appear in the Dock or ⌘Tab.
• Click the menu bar numeric to open a popover with:
  • Per-core CPU temperatures
  • A 5-minute history chart for the primary core
  • Fan RPMs (hidden on Macs without fans, e.g. MacBook Air)
  • A Settings section: two sliders for the green→yellow and yellow→red thresholds, plus a °C / °F unit toggle
  • A Quit Specter button

Run as a standalone app on this Mac

For personal use, no signing or notarization is required — Xcode's default "Sign to Run Locally" identity is enough.

# Build a Release binary
xcodebuild -project Specter.xcodeproj -scheme Specter -configuration Release build

# Link it into /Applications so it's stable across rebuilds
ln -sf ~/Library/Developer/Xcode/DerivedData/Specter-cojnreaiwmjnpgdolqhjyisxslkv/Build/Products/Release/Specter.app /Applications/Specter.app

# Launch it
open /Applications/Specter.app

The first launch may show a Gatekeeper prompt about an unidentified developer. Right-click the app in Finder → Open to bypass it once; macOS remembers the choice.

To launch Specter at login: System Settings → General → Login Items → + → add Specter.

Verifying the reading

Compare against powermetrics (requires sudo):

sudo powermetrics -s smc -i 1000 -n 1 | grep -i "CPU die temperature"

The menu bar value should agree within ±2 °C.

Settings persistence

Settings live in UserDefaults under the com.specter.app domain. To inspect them:

defaults read com.specter.app

Keys:

• greenYellowThreshold — Double, stored in °C
• yellowRedThreshold — Double, stored in °C
• unit — String, "C" or "F"

To reset to defaults:

defaults delete com.specter.app

Architecture

App/         — AppDelegate (AppKit entry point) + Info.plist (LSUIElement = YES)
SMC/         — SMCKit key constants (Tp09, Tp01, F0Ac, …)
Telemetry/   — TelemetryProvider protocol, SampleStore ring buffer,
               TelemetryService (1 Hz timer), CPUTemperatureProvider, FanSpeedProvider
Popover/     — PopoverView, PopoverViewModel, SettingsSection, MetricRow, SparklineChart
Settings/    — Settings value type + SettingsStore (UserDefaults wrapper)
UI/          — MenuBarController (NSStatusItem), PopoverController (NSPopover)

The data flow is: TelemetryService ticks once per second, calls each provider's async sample(), appends to a per-provider SampleStore, and fires onUpdate. MenuBarController reads the latest sample to redraw the menu bar; PopoverViewModel reads the same store to build immutable snapshots for the popover. No mutable state crosses the boundary into SwiftUI — the view tree only sees ProviderSnapshot values, and re-renders are triggered by @Published mutations on the view model.