How Charger Removal Alarm Works Across Platforms

Building a lightweight application that functions perfectly across multiple operating systems is no small feat. In this article, we take a deep dive into the technical mechanics of the Charger Removal Alarm and how it integrates with native power state APIs on Windows, macOS, and Linux.

The Architecture: Native Bindings vs Polling

Many power-monitoring tools rely on constant polling—checking the battery status every few seconds. This is bad for battery life and CPU usage. Instead, Charger Removal Alarm uses a push-based architecture. We register callback functions directly with the kernel-level power APIs of each operating system so that we are only woken up when a change actually occurs.

1. Windows Integration (Win32 API)

On Windows, we register for power notifications using the Win32 API. Specifically, we call RegisterPowerSettingNotification with the target GUID set to GUID_ACDC_POWER_SOURCE.

When the user unplugs their AC adapter, Windows broadcasts a WM_POWERBROADCAST message to our hidden window handle, passing the parameter PBT_POWERSETTINGCHANGE. Our app intercepts this message instantly, triggering the alarm logic.

2. macOS Integration (IOKit & IOPowerSources)

Under macOS, the application hooks into the Apple IOKit framework. We register a notification port using IONotificationPortRef and hook into the power source notification loop.

We utilize the IOPSCreatePowerSourceRunLoopSource system API. This provides a run-loop callback whenever the system switch is made between "AC Power" and "Battery Power". Since this runs on Apple's native CoreFoundation run-loop, resource usage is practically zero.

3. Linux Integration (D-Bus & UPower)

On Linux, our service communicates via the system D-Bus. We listen for properties changes on the UPower service, which monitors power devices:

By subscribing to the PropertiesChanged signal, we receive an event the split-second the battery state flips to discharging. This supports all modern desktop environments, including GNOME, KDE Plasma, and XFCE.