Android secret codes: hidden dialer menus that actually work

The two that earn their reputation are *#*#4636#*#* and *#0*#. The testing menu gives you a real signal reading in dBm rather than the bars on the status bar, which is genuinely useful for diagnosing a phone that keeps dropping calls. The Samsung hardware test runs through every sensor in turn and is the fastest way to check a used handset before buying it.

Open the Phone app and type the code into the keypad exactly as written, including every star and hash.

Most engineering codes open the moment the last character is typed — you do not press call. Network codes, the ones that start with a double star or double hash, are the opposite: those need the call button to be sent to the carrier.

If nothing happens at all, the code is disabled on that handset. There is no workaround short of a different phone, and no dialer app can re-enable a code the manufacturer removed.

*#*#4636#*#* then Phone information gives you the actual signal figure in dBm. Reading it:

• Better than -85 dBm is a strong signal
• Between -86 and -100 dBm is workable
• Between -101 and -110 dBm is weak, expect dropped calls
• Below -110 dBm is effectively no usable service

This matters if calls keep failing in one part of a building. The bars in the status bar are a rounded marketing figure and vary between manufacturers; the dBm number does not. If you are diagnosing calls that ring once and stop, though, check the settings first — why is my phone not ringing covers the causes that look like signal problems but are not.

Several widely circulated Android codes trigger a factory reset or a full wipe with no confirmation prompt. Dial one by accident and the phone erases itself immediately — no undo, no warning dialog, and on some devices it also formats the SD card.

We do not list those, on this page or on the USSD code list. Any list that publishes them next to harmless diagnostic codes, with no distinction between the two, is worth closing.

One related warning: codes claiming to unlock a carrier-locked phone, raise your data speed, or reveal a hidden network setting do not work. Carrier unlocking is an account-level request to the carrier, not something a dialer string can do.

The codes above talk to the handset. A second family talks to your carrier's network — call forwarding, caller ID, and status checks — and those work on any Android phone regardless of manufacturer:

Those are carrier codes rather than Android codes. The complete set is on the USSD code list, with per-carrier variations under AT&T codes, Verizon codes and T-Mobile codes.