I Use These Secret Codes to Test Used Android Phones Before Buying Them
Used phones sometimes have faulty hardware that might escape basic inspection. That’s why I recommend running top-to-bottom diagnostics on the phone before you hand over the cash. Thankfully, Android phones have secret codes for doing just that.
Why You Should Be Using Secret Codes to Test Used Phones
A few years back, I bought a second-hand Android phone whose fingerprint scanner stopped working after a while. It worked as expected during the initial purchase, but when I brought it home, it wouldn’t pick up my fingerprint. Turns out, the scanner only stays active a short while after rebooting the phone. In retrospect, I should have learned whether used phones are worth buying in the first place.
I had also seen friends and family pick up phones with dead pixels, dead touch zones, and all kinds of networking issues. Since then, I’ve been using secret Android codes to test used phones. While secret codes aren’t the only way to test phones—you can find plenty of apps on the Play Store to do the job—I recommend you use them for a few reasons:
- Third-party apps aren’t always reliable or comprehensive.
- Grabbing apps from the Play Store requires signing into your Google Account, which is a hassle on a phone that hasn't been set up yet.
- The secret codes launch built-in diagnostic tools made for the express purpose of testing hardware quality.
The testing tools contain hidden settings that aren’t available in the regular settings app. To launch them, you need to punch a secret code into the dialler app. Since these tools aren’t user-facing, the codes are not officially made public.
Where to Find the Codes
Some of the codes can be slightly different depending on the manufacturer of your phone. We'll be using a Redmi phone in this guide, which shares the same code with Xiamo and POCO phones. Here are a few of the codes for popular Android brands to open the "Diagnostics Mode."
- Samsung Galaxy: ##4636##
- Google Pixel: * # * # 7287 # * #*
- Motorola:
