Plugged

Ports Gone Wild

What is this

Plugged is a tiny macOS menu-bar app that watches what you plug into your Mac and tells you when something changes.

• Plug in a charger? It shows the wattage.
• Unplug it? It tells you how much battery you’ve got left.
• Connect a dock or USB device? You get a quick heads-up about what just appeared.

How it works

Plugged is fully event-driven. It does not poll or continuously scan the system. Instead, it listens for low-level macOS system events and reacts immediately when something changes.

USB events (connect / disconnect)

USB device changes are handled using IOKit and the I/O Registry.

Plugged registers for USB notifications by matching IOUSBHostDevice services:

• IOServiceMatching("IOUSBHostDevice") Creates a matcher for USB devices in the I/O Registry.

• IOServiceAddMatchingNotification(...) Registers callbacks for when matching USB services appear or disappear.

• IOIteratorNext(...) Iterates over devices that triggered the notification.

• IORegistryEntryCreateCFProperty(...) Reads device properties such as:

  • product name
  • vendor ID (VID)
  • product ID (PID)
  • connection speed

When a device is plugged in or unplugged, macOS immediately triggers the callback. Plugged extracts the device information and updates:

• the menu-bar device list
• user notifications

No polling is used. All USB updates are event-based.

Power events (charger / wattage / battery)

Power changes are monitored using the Power Sources API from IOKit.

• IOPSCopyPowerSourcesInfo() Takes a snapshot of the current power source state.

• IOPSCopyPowerSourcesList(...) Lists available power sources (battery, external power).

• IOPSGetPowerSourceDescription(...) Reads details such as:

  • charging state
  • current capacity
  • maximum capacity
  • power source type

Charger wattage is read from adapter-related system properties through a small wrapper around IOKit power information.

When the power state changes:

• Charger connected → negotiated wattage is shown
• Charger disconnected → remaining battery percentage is shown

Notifications

User notifications are delivered using UserNotifications.

• UNUserNotificationCenter.requestAuthorization(...) Requests notification permission once.

• UNUserNotificationCenter.add(...) Posts notifications for:

  • USB device changes
  • dock / hub connection bursts
  • charger connect / disconnect events

To ensure notifications appear even while the app is active:

• userNotificationCenter(_:willPresent:) returns .banner

Menu bar UI

The menu bar interface is built using standard AppKit APIs:

• NSStatusBar.system.statusItem(...)
• NSMenu for the dropdown menu
• statusItem.button for icon and title updates

The app runs as a menu-bar agent only:

• LSUIElement = true

This prevents Dock icons, windows, and app-switcher entries.