Best free apps and tools to check a used Android phone
No single tool sees everything. This is what each kind of tool is good for when you are buying or selling a used Android phone.
Knowfone: a buy-or-not answer
Knowfone is built for the moment of buying. It tests identity (is it the model it claims), security, every part of the touch screen, the display, speakers and microphones, cameras, battery, processor, storage, sensors, buttons, charging port and radios, then says good to buy, buy only at a lower price or don't buy, with the reasons. Free, no account, about 7 minutes. Sellers can share a certificate with a QR code.
Spec and sensor viewers
Device information apps such as DevCheck or CPU-Z show the processor, memory, sensors and battery readings in detail. Good for experts who know what numbers to expect; they do not tell you whether to buy.
Battery trackers
Apps that measure battery capacity over several days of charging give an exact number, but only after you own the phone.
Built-in tools
- *#06# in the phone app shows the IMEI; compare it with the box.
- *#0*# opens a hardware test menu on many Samsung phones.
- Samsung Members, Phone diagnostics checks many parts of Samsung phones.
- Developer options, Pointer location draws your touch to find dead zones.
Professional certification
Shops and refurbishers use paid systems such as Phonecheck to grade and certify phones in bulk.
What no tool can check
Past water damage, repairs inside and whether a phone is stolen or blocked need the box, the receipt and a check with the network operator.