My brother-in-law was about to pay a repair shop $80 to diagnose why his phone screen had a dead spot. I opened the phone dialer, typed a short code, and the phone ran its own diagnostic — testing the screen, speakers, vibrator, and sensors — right in front of him. The repair shop wanted $80 for something the phone can do for free in two minutes.

Most Android phones have a hidden diagnostic menu accessible through dialer codes. Here is what it tests and how to use it.

The universal code: *#0*#

Open your phone dialer like you are making a call. Type *#0*# and the diagnostic menu appears — no call button needed, it just opens. (If it does not work, your phone manufacturer may have disabled it — Samsung, Motorola, and most unlocked phones support it. Some carriers block it on branded devices.)

The menu shows colored tiles for different tests: Red, Green, Blue (screen pixel test), Receiver (earpiece speaker), Vibration, Dimming, Touch (draw on the screen to find dead spots), Sensor (accelerometer and proximity), and more.

What each test does

• Red / Green / Blue — Fills the screen with one solid color. Dead pixels, screen burn-in, and uneven backlighting are instantly visible.
• Touch — Draw lines with your finger across the screen. Any gaps in the lines mean dead touch zones.
• Sensor — Shows real-time readings from your accelerometer, gyroscope, and proximity sensor. Tilt the phone and watch the numbers move.
• Vibration — Vibrates the phone so you can check if the motor works.
• Speaker / Receiver — Plays a tone through each speaker so you can check sound quality.

Other useful codes

*#06# shows your IMEI number — useful if your phone is stolen and you need to blacklist it. *#*#4636#*#* opens a detailed usage statistics menu showing battery health, WiFi signal strength, and app usage data. This one works on almost every Android phone.

Press the back button to exit any test. None of these codes can damage your phone — they are read-only diagnostic tools built in by the manufacturer.