Lenovo Pen Plus Debug

An investigatory tool for detecting and displaying Lenovo proprietary stylus button events on Lenovo Idea Tab Pro

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What?

I first tried to detect the opening and closing of the pen toolbox that Lenovo's OS offers (not a very good method) using accessibility (which did not work lol). Then I decided to check adb logcat output for any stylus related event. I did not find it being related to stylii styluses, but I did find Bluetooth logs. This led me to the finding that the button on the pen is not a HID button, but rather a Bluetooth button (like the buttons found for control in audio devices).

I first used Shizuku (ADB-level access) to monitor logcat output from the Android framework's BluetoothPenInputPolicy class, then found KeyEvents being fired in the same logcat output, so later added a detection for the firing of those events and read the gesture type by the keyCode (which was mapped by experimentation).

Detection Methods

Direct observation via logcat parsing

• Monitors BluetoothPenInputPolicy framework logs
• Detects keycodes: 600, 601, 602, 603, 604
• Parses clickStatusType: 0=Single, 1=Double, 2=Triple, 3=Long Press, 4=Long Press + Click

Shizuku Logcat Parsing:

Log Format Parsed:

12-25 10:30:45.123 D/BluetoothPenInputPolicy( 1234): processStylusPenKeyEvent: keycode 602,mIsStylusPenRemoteControl false,clickStatusType 2

Extracted Data:

• keycode: 600/601/602/603/604 (vendor-specific)
• clickStatusType: 0=Single, 1=Double, 2=Triple, 3=Long Press, 4=Long Press + Click

No root required to read these logs.

KeyEvent based detection

The app hooks Lenovo’s vendor keycodes in MainActivity.onKeyUp() and treats keyCodes 600..604 as “pen button events”. It checks if (keyCode in 600..604), maps each code to a label, logs it, then calls viewModel.addKeyEventDetection(keyCode) and returns true to consume the event.

Only code 601 produces both ACTION_DOWN and ACTION_UP, while 600/602/603/604 are ACTION_UP only. Detecting in both onKeyDown and onKeyUp would double-count 601, so I removed onKeyDown and detect only on key-up.

This works only when the activity is in the foreground. A class: dev.ilamparithi.lppdebug.LenovoPenButtonListener is included to serve as an example for usage in other apps. It does not have any dependencies. I created a patch for termux-x11 for my personal use. Please feel free to modify and use the patch as required, to add this detection in termux-x11.

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What the app shows

• Last Detected Event: Large display showing the most recent button press
• Click Type: Single/Double/Triple/Long Press/Long Press + Click
• Timestamp: Precise time of event
• Event History: Scrollable list of past 100 events
• Keycode: Vendor-specific keycode (600-604)

Limitations

This app cannot:

• Intercept the lenovo.intent.action.INPUT_DEVICE_CLICK_STATE_CHANGED broadcast (protected by system)
• Prevent default Lenovo toolbox behavior (you can still disable it in settings)
• Inject custom actions on button press
• Access vendor-specific framework APIs

Why These Limitations Exist:

1. Protected Broadcast: The lenovo.intent.action.INPUT_DEVICE_CLICK_STATE_CHANGED intent is part of the protected-broadcasts, making it impossible for third-party apps to receive
2. Framework-Level Processing: Events are handled at the Android framework level before reaching app layer

It cannot modify stylus behavior.

Tested with

• Lenovo Idea Tab Pro + Lenovo Pen Plus stylus

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Setup Instructions

Step 1: Install and start Shizuku (optional)

1. Download and install Shizuku from Google Play or GitHub
2. Open Shizuku app
3. Follow the setup wizard to start Shizuku service

Step 2: Install this app

1. Build and install the APK (or grab a build from releases):

   ./gradlew assembleDebug
   adb install app/build/outputs/apk/debug/app-debug.apk
   

2. Open "LenovoPenPlusDebug" app

Step 3: Grant Permissions (optional)

1. The app will show "Permission Required" status
2. Tap "Grant Shizuku Permission"
3. Shizuku will show a permission dialog
4. Tap "Allow"

Step 4: Start Monitoring

1. Tap "Start Monitoring" button
2. Status indicator will turn green: "✅ Monitoring Active"
3. Press any button on your Lenovo Pen Plus
4. Check if the event gets logged on screen

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