Android smartphones dominate the second-hand mobile market in Bangladesh, offering incredible value across brands like Samsung, Xiaomi, Google Pixel, OnePlus, Vivo, and Realme. However, because Android hardware varies widely, knowing exactly what to test during a physical inspection is critical.
Use this comprehensive 10-step inspection routine during your next in-person meetup to ensure you walk away with a flawless Android device.
Hardware Diagnostic Secret Codes
Most major Android manufacturers include built-in engineering diagnostic menus that test every sensor and pixel in seconds. Dial these codes in the default phone app:
| Brand | Secret Diagnostic Code | Menu Function |
|---|---|---|
| Samsung | *#0*# |
Hardware Diagnostic (Screen RGB, Touch Grid, Vibration, Subkey, Cameras) |
| Xiaomi / Redmi / POCO | *#*#6484#*#* or tap "Kernel Version" 5 times |
CIT Hardware Test Suite |
| OnePlus / Oppo / Realme | *#899# |
Engineer Mode Manual Diagnostics |
| Google Pixel / Motorola | Download "Device Info HW" from Play Store | Complete sensor, panel manufacturer & battery status |
The 10-Step Physical Testing Routine
Check for AMOLED Screen Burn-In & Green Lines
Open a solid white and a solid red image in full screen. AMOLED panels (especially on older Samsung and OnePlus devices) can suffer from permanent burn-in from the TikTok interface, YouTube status bar, or keyboard. Also inspect carefully for thin vertical green or pink laser lines.
Test the Touch Screen Grid
In the Samsung *#0*# or Xiaomi CIT menu, open the Touch Grid test. Draw continuous lines across all boxes until every square turns green. If any block fails to color, that specific sector of the digitizer is damaged.
Verify All Camera Lenses & Autofocus
Switch between all individual camera sensors: Main, Ultra-wide, 3x Telephoto, and Macro. Tap on nearby text and distant scenery to confirm autofocus locks instantly. Shake the phone gently while viewing the preview to check that Optical Image Stabilization (OIS) doesn't produce blurry waves.
Inspect the USB-C Port & Fast Charging
Plug in a fast charger or power bank. Look for the "Fast Charging" or "SuperVOOC / Turbo Charge" indicator on the lock screen. Slightly wiggle the cable connector: if charging disconnects or flashes, the internal port pins are loose or corroded.
Test Dual SIM Slots & Cellular Data
Insert SIM cards into both SIM 1 and SIM 2 slots. Confirm that both slots recognize 4G/5G networks, make a successful voice call on both, and verify internet browsing speeds.
Check Microphones & Earpiece Quality
Record a 10-second voice note using the preinstalled Voice Recorder app while speaking normally. Play it back at full volume through the bottom speakers and through the top earpiece to check for distortion or crackling audio.
Test Fingerprint & Face Unlock Sensors
Register both thumbs on the in-display or side-mounted fingerprint scanner. Lock and unlock the device 5 consecutive times to test reliability. If an optical or ultrasonic in-display scanner is slow or fails, the screen may have been replaced with a low-grade TFT copy.
Inspect Body Frame & Water Resistance Seals
Check the seam around the back glass and front display. If you see sticky glue residue, uneven gaps, or lifting edges, the phone has previously been opened for internal repairs.
Remove Google FRP & Brand Accounts
Ensure the seller navigates to Settings > Accounts and removes all Google accounts, Xiaomi Mi accounts, and Samsung accounts. If an account remains linked when factory resetting, the phone will lock permanently upon reboot.
Perform a Full Factory Reset On-Site
Finally, perform a complete Factory Data Reset in front of the seller. Wait for the phone to reboot to the initial language setup screen to guarantee that no hidden remote management software is active.