(Credit; Zain bin Awais)
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.
(Credit: PCMag)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.
(Credit: PCMag.com)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). On an iPhone, you can change this number in Settings > Phone > Call Forwarding. On Android (varies by system), tap the Phone app > three-dot menu > Settings > Calling accounts, pick your in-use SIM card, then find call forwarding. This obviously means calls won't go to your mobile carrier's voicemail, but if the number you put in has voicemail, the caller can leave a message there.
(Credit: PCMag)Call Waiting: 43 (Various Combinations)
Call waiting, of course, is how you can know there's another call coming in when you're already on the phone.
In testing, I found that on AT&T, using *#43# deactivated a slew of things—voice call waiting, data call waiting, fax call waiting, SMS call waiting, and sync data circuit call waiting (whatever that is). I reactivated the voice call waiting specifically with *#43#, and confirmed it in the iPhone's Settings > Phone > Call Waiting menu. It should be the same code for T-Mobile.
On Verizon, using *43 will deactivate call forwarding, not call waiting; *42 will turn it back on. To temporarily stop call waiting on Verizon, use *70 before the 10-digit number you call.
(Credit: PCMag)Available Minutes: 646
The 646 on the keypad also spells out "MIN." With an iPhone on AT&T, the code 646# returns an SMS text message revealing how many minutes are still available. Same on Android: Instead of showing the info on a new screen, it sent a text. AT&T also offers an option for Spanish speakers via *876#. Verizon says to use #646; T-Mobile uses #646#. You can replace the 646 with the letters MIN in any of the cases above for the same response. Note that you may get an error if you have unlimited talk on your plan.
(Credit: PCMag)Billing Cycle: 3282
This prompts an SMS message with billing info, including when the billing cycle started, total plan usage (even by line if your account has more than one), and if you've gone over your data allotment. (3282 spells "DATA.")
Even if you have "unlimited" data, this can be handy since some carriers will deprioritize your connection if you reach a high threshold of use (say, after 100GB of downloads on a phone in a month).
Like above, each carrier has its own format: AT&T is *3282# (or *DATA#). Verizon is #3282 (or #DATA). T-Mobile goes with #932# (or #WEB#).
(Credit: PCMag)Caller ID: #31# or *67
Entering *#31# displayed a screen stating that my Caller ID (also known as Calling Number Display or CND) had been disabled ("ID Restriction: Disabled" means your number is visible). To reinstate Caller ID, enter *31# or do it under Settings > Phone on iPhone.
This code may be better known to some people as a way to block caller ID on a per-call basis. Type #31# (or the more familiar *67 for the US; 31 is the Global GSM standard) before you put in a person's 10-digit number. What you enter would look like #31#1234567890. This is a must on landlines, where you can't turn off Caller ID without asking customer service.
If your mobile device's caller ID is always turned off, you can reactivate it on a single call by entering *31$ or *82 before the number.
(Credit: PCMag)Test Alert Status: *5005*25371#
Specific to iPhones in the US, this will tell you if your iPhone is set up to receive test alerts from the government and emergency services, specifically FEMA and the FCC. Again, this isn't for the actual alerts—it's just to test if you can get them. Dialing the number above will give you a yes or no. If it's on and you want it off, dial *5005*25370# and hit the call button to disable alerts. Newer iPhones can toggle this on or off in Settings > Notifications (scroll down to "Government Alerts").
(Credit: PCMag)By the way, you cannot turn off "National (Presidential) Alerts" issued by the White House or FEMA, which are reserved for a catastrophic national emergency.
Check Account Balance: *777# (Prepaid) or *225# (Contract)
If you've got a prepaid phone on AT&T, dialing *777# and hitting the call button generates a text message showing how much you have left. If you don't have a prepaid phone, it will say you have the wrong type of account.
(Credit: PCMag)Instead, use 225 (it spells "BAL") to look up your contract (postpaid) phone balance. This is sends a text message with your current billing balance due.
For AT&T use *225#. On Verizon, it's #225. T-Mobile users use #225#. The latter two can use 225 for prepaid and postpaid phones.
(Credit: PCMag)Android Phone Stats: *#*#4636#*#*
This code spells spells *#*#INFO#*#*. It brings up a Testing settings panel with 5G/LTE debugging info, phone information, usage statistics, Wi-Fi information, and NFC settings. How much of it you can understand may vary. The data includes signal strength, network type, force network mode (forcing a phone to use only 4G or only 5G), and more. This code is usually disabled on Samsung phones, but you can try *#0011# for "Service Mode."
(Credit: PCMag)Call Barring: *#33#
Call barring literally lets you block any and all outgoing cell calls. You can do it in the settings on an Android device, but this number applies to your account. Dialing *#33# shows you the status, if the feature is even available with your carrier. To enable it, you'd need to know the PIN for your actual SIM card (the default is often 0000, 1111, or 1234) or your eSIM. If you know the old PIN and want to change it try this sequence: **03*[OLD PIN]*[NEW PIN]*[NEW PIN]#.
This feature is often blocked by carriers and will bring up an error. But you can try it: type *#33*[SIM-PIN]# to activate it, or type it again to deactivate. With some carriers, you can choose specific kinds of calls to bar, such as international calls, roaming calls, even specific numbers. The last option is probably easier to do on a case-by-case basis. Read How to Block a Number on Your iPhone or Android Device.
To block incoming calls, use *#35#. This is a "do not disturb" feature, but on the network level.
(Credit: Apple/PCMag)Read the Regulations: *#07#
Dialing this code takes you directly to the legal and regulatory information for your phone model. On the iPhone, you can also access it by going to Settings > General > Legal & Regulatory. From there, you can go deeper to find legal notices, warranty info, and even radio frequency exposure warnings.
(Credit: PCMag)Wipe Your Android Device: *2767*3855#
We did not test this one. If you type it into an Android device, specifically Samsung phones, it reportedly performs a full factory reset/restore, even reinstalling the phone's original firmware. Use at your own risk! It is supposedly instantaneous and irreversible.
That's the nuclear option. But there's a less aggressive "Factory Data Reset" option, ##7780#*#*, which removes your Google account and downloaded apps. Or you can do that in Settings > System > Reset Options.
The Information You Need: N11 Codes
Don't forget that in the US you can always call the N11 codes—a digit followed by 11—for information delivered audibly:
- 211 - essential community services; call it for help with utilities and housing
- 311 - municipal government services, like getting trash collection schedules or reporting problems like potholes
- 411 - directory assistance; there could be a fee involved to get a number this way, so you'd be better off searching online first
- 511 - information on local traffic, where available
- 611 - telephone company customer service (works with most mobile carriers)
- 711 - TDD/TYY services for the deaf
- 811 - Dig Safe; call it before you dig deep holes where utility lines or pipes may be hidden
- 911 - local emergency services
Do you know of any dialer codes that work on modern smartphones that we've missed? If so, leave them in the comments below!
Evan Dashevsky contributed to this story.