Mercury

Tiny macOS menu bar temperature monitor built with SwiftUI and IOKit.

[swift, swiftui, iokit, homebrew] source ↗ writeup →

overview

Native macOS app using SwiftUI for UI and IOKit for direct SMC temperature reads. Monitors CPU, GPU, and battery temperatures. Dynamic menu bar icon reflects thermal state. Distributed via Homebrew cask.

challenges

Reading SMC sensor data directly from macOS kernel
Supporting both Apple Silicon and Intel sensor key mappings
Keeping CPU usage minimal with continuous polling

solutions

Direct SMC reads via IOKit with sub-millisecond sensor polling
Auto-detection of available sensors per chip architecture
Configurable refresh interval (1-10s) with <1% CPU at default rate

learnings

IOKit — direct SMC communication for hardware sensor data
macOS menu bar app architecture — no dock icon, no windows
Homebrew cask distribution and CI/CD with GitHub Actions
Apple Silicon vs Intel SMC key differences