PowerMonitor

I was on a flight that only had a USB power outlet, and I didn't know whether I was drawing more power than I was receiving. So I built this.

A single-file SwiftUI menu bar app for macOS. Event-driven via IOKit — near-zero CPU when idle.

Install

git clone https://github.com/jlreyes/PowerMonitor.git
cd PowerMonitor
make install
open -a ~/.local/bin/PowerMonitor.app

Auto-start on login

make launchd-install

To remove:

make launchd-uninstall

How it works

• Registers an IOPSNotificationCreateRunLoopSource callback that fires on any power source change
• Reads AppleSmartBattery via IOKit for voltage, amperage, charging state
• If ExternalConnected == true && InstantAmperage < 0 — you're draining while plugged in
• Sends a native macOS notification (5-min cooldown) when this happens

Menu bar states

Icon	Meaning
⚡ 9W	Plugged in, charging at 9W into battery
⚠ 5W	Plugged in, draining at 5W (charger can't keep up)
63%	On battery

Requirements

• macOS 13+
• Swift 5.9+

License

MIT