Type in a few numbers and symbols on your dialer and discover powerful tools, system info, and settings buried deep in your phone.
For almost as long as personal computers have existed, coders have created backdoors in programs (or sometimes just fun little Easter eggs) that can only be accessed with a special “key.” The tradition continues in the mobile age.
You can use many of these mobile backdoors yourself via Unstructured Supplementary Service Data (USSD), sometimes known as “quick codes” or “feature codes.” It’s an extra-UI protocol that allows people to access hidden features. It was originally created for GSM phones, but it’s still used in many 4G and 5G devices today. There are also what are called Man-Machine Interface (MMI) codes, which phone manufacturers make specifically for their own devices.
These publicly available codes allow users to directly communicate with their service provider’s computers and access back-end features on their devices. They can be accessed by entering them into the phone’s dialer (the screen you use to start a phone call) and usually begin and end with the * or # keys, with a sequence of numbers in between. This way, there’s a close-to-zero chance that anyone would accidentally punch them in.
Just be warned: They’re not terribly practical. Most of these codes simply surface data that the average person doesn’t really need, like how nearby cell towers are performing, or what your IMEI number is (more on that later). Still, it can be fun to play around and see what unexpected functionality your phone is hiding. Tread carefully, though; some of these codes can be dangerous to your phone—particularly anything that has the word “wipe” in the title. Don’t erase your smartphone just for the sake of experimentation!
Furthermore, while we would love to provide you with a comprehensive list of the dozens of codes out there, doing so would be an exercise in futility. These codes seldom work across different carriers, OSes, or phone models (or even on different models from the same line). Carriers also don’t want regular customers using these codes and often deactivate or change them as needed.
If you want to try them out, first do a web search of your phone’s make and carrier + “USSD” or “MMI” for a tailored, comprehensive list. Don’t be surprised if many of them no longer work. We attempted several codes using an iPhone 15 Pro and more on Motorola and Samsung handsets. The list of codes that got a response on at least one device appears below. Have fun!Field Test Mode: *3001#12345#*
Type this code into your phone’s dialer, then press the green call button to enter “Field Mode”, which shows information about local networks and cell towers, as well as your phone’s signal strength. Unfortunately, this info will not reveal whether someone is tapping your phone. Almost all of it is incomprehensible data meant only for technicians. To help yourself, read about how to improve signal strength.IMEI Display: *#06 The International Mobile Equipment Identity number or IMEI is unique to your device and links it to a specific network. Among other things, the number can help “blacklist” stolen devices or assist with customer support. If you have multiple SIM cards or a dual-SIM or eSim in your phone, you may have more than one IMEI, as shown below. On an iPhone, you can also find the IMEI in Settings > General > About, but typing *#06# works across platforms, so it’s faster for techs.Call Forwarding: *#67# and *#21 These codes allow you to check which number your phone is currently forwarding calls to when you’re busy or reject a call. The first is for forwarding when you’re busy on a call; the second is “unconditional”, so it forwards all calls, meaning your phone never rings.
By default, the number you’ll see by dialing *#67# is probably your carrier’s voicemail service (the number below is for the Voicemail Call Center for AT&T Mobility), but you can change it to forward to a different number (a home number, office number, or third-party answering service, for example).
