ChillPill

A macOS menu bar app that shows internal temperatures and controls fan speed, without hard-coded elevated privileges for the UI.

Status: alpha — the core read/write path works end-to-end on an M1 Pro 14" MacBook Pro. Tracked open issues: #3 (split CPU group into P-cores / E-cores).

Requirements

• macOS 13 (Ventura) or newer — tested on macOS 26 (Tahoe)
• Apple Silicon (M-series) — Intel Macs are untested
• Xcode Command Line Tools (xcode-select --install)

No Homebrew dependencies. No Xcode project (SPM-driven).

Build & run

git clone https://github.com/Snoww3d/ChillPill.git
cd ChillPill
make
open build/ChillPill.app

On first launch macOS shows a "Background Items Added" banner. To enable fan control, go to System Settings → Login Items & Extensions and toggle ChillPill on. This approves the bundled helper daemon — after that, no password prompts, including across reboots.

To install to your user applications folder:

make install          # copies the release build to ~/Applications/
open ~/Applications/ChillPill.app

How it works

The project is split across three SPM targets:

Target	Role	Runs as
ChillPill	Menu bar UI; no IOKit / SMC code	user
ChillPillHelper	SMC read/write, fan control, sensor enumeration	root
ChillPillShared	XPC protocol + Codable DTOs	n/a

The UI and helper communicate over an NSXPCConnection against a registered Mach service. Fan control commands carry only indices and target RPMs — the helper validates input bounds, clamps to the advertised [min, max] range, and only ever writes the F{n}Md and F{n}Tg SMC keys (enforced by construction — no generic "write any key" method exists on the XPC surface).

Temperatures come from two sources which the helper merges:

• IOHIDEventSystemClient → per-die sensors (P-cores, E-cores, GPU, SoC, PMIC, ANE, ISP, battery, NAND). Friendly names from the research in Sources/ChillPillHelper/Sensors.swift.
• AppleSMC FourCC keys → location-based thermistors (palm rest, airflow intakes, wireless, SSD area). Discovered at startup by enumerating the SMC key table.

Uninstalling

From the menu: ChillPill → Uninstall Helper — calls SMAppService.daemon.unregister(), which removes the launchd job. Or, manually, in System Settings → Login Items & Extensions, toggle ChillPill off.

Disclaimer

Fan-control software pokes at undocumented hardware interfaces. Bugs here could in principle cause overheating or odd thermal behaviour. Use at your own risk — no warranty (see LICENSE). On app quit (including SIGTERM / SIGINT), the helper restores all fans to auto as a belt-and-braces safety net; kill -9 bypasses this.

License

MIT.