USB and Bluetooth: understand trust

Understand it

The Flipper can present itself as a human interface device, such as a keyboard. The computer receives keystrokes; it does not infer the author’s intent. The application’s “Bad USB” name describes a class of risks, but a script can be as small as typing a sentence.

This exercise types only text into an editor that you open yourself. It contains no shell commands, downloads, credential access, or system changes. Keyboard layout and the currently focused window affect what happens. Read any script in full before using it.

REM Signal Path: visible typing in your own text editor
DELAY 3000
STRING Signal Path - I control this lab.
ENTER

Bluetooth is a separate interface

BLE pairing establishes a relationship with a specific device. Pairing your Flipper with its mobile app is different from pairing keyboard emulation. Record which function you are enabling. The internal Sub-GHz radio does not turn into Wi-Fi through a firmware change; Wi-Fi experiments need separate compatible hardware and their own lab scope.

Lab: build the evidence

1. On your own computer, open a blank plain-text document. Copy the four-line example into a separate ASCII file named signal-path-hello.txt. Read every line.
2. Copy that file into the Flipper SD card’s badusb folder using qFlipper. Close qFlipper before starting the HID session.
3. Choose the file in the Bad USB app and select USB mode. Confirm your keyboard layout. Connect to your computer, focus the blank document, and run once while watching the screen.
4. Expected result: one sentence and a newline after three seconds. If the wrong window has focus, disconnect immediately. Re-focus the editor before any retry.
5. Disconnect, delete the disposable document, and remove the exercise file if you no longer need it.
6. Optional: pair your own phone using the official mobile app, confirm the displayed code on the intended devices, then practise removing that pairing. Do not scan or connect to strangers’ devices.

Show that you can do it

• The exact text output, without executing any operating-system commands.
• An explanation of focus, layout, USB HID, and why script review matters.
• A note identifying your own pairing and how you removed it.

Record the result in your learning notebook. Repeat the explanation tomorrow without looking at this page.

Check yourself

Sources

Read the primary sources: Flipper: USB and BLE keyboard emulation · Flipper: first start. Course review: 10 September 2026.