Smartphones are complex little machines. With the right apps downloaded, a person can trade stocks, play games, and produce music all on the same machine that is used for making and receiving phone calls. It would seem that the phone app on a smartphone is the least complicated app there is. That theory is about to be shattered.

The dial pad on a cell phone is like a door to another electronic world. Most people simply don’t have the key to it. Although the exact codes vary by phone type and service provider, every cell phone has the capability to use Unstructured Supplementary Service Data (USSD) codes. To put it simply, these codes are essentially a way for people to send text messages to cell towers and cell phone service providers. These “text messages” are the set of USSD codes that are unique to each phone. When one of these codes is typed into the dial pad of a cell phone, the phone interacts with the background user interface to display a “reply” to the “message.” There is a strict set of messages and replies. 

As high tech and strange as these codes may sound, the concept is really one that is familiar. Although it wasn’t necessarily part of the same code system, back in the days of landline corded phones, it was common to dial codes like *69 to find out who just called. In the earliest days of cell phone use, most people were on prepaid plans or plans that only allowed a certain number of minutes and texts per month. Many cell phone service providers had specific codes, often starting with an asterisk, that customers could dial to find out how many minutes they had left from the month. USSD codes are very similar. Although they are much longer than the shorter codes most people are used to, USSD codes often begin with an asterisk and end with the pound (also known as a hashtag) symbol. Some USSD codes can get behind the scenes information about a cell phone service provider, but others do pretty simple things. Here a few codes that might be useful.

Block caller ID

Code: #31#

How to stop it: *31#

Works best on: Androids

Function: Most phones show a confirmation message after this code has been entered to let the user know that his or her number will not be shown on the caller ID of the receiver of any calls made from the phone. This a great feature to use to hide the caller’s phone number from the receiver of the call. It’s very easy to toggle this feature on and off as much as necessary.

Turn call waiting on

Code: *43#

How to stop it: #43#

Works best on: All phones

Function: Most newer cell phones have call waiting built in. It just has to be turned on, which can be complicated depending on the type of phone. This USSD code can be used as an easier way to activate the feature. Call waiting allows a user to place an ongoing call on hold to answer an incoming call.  After hanging up the second call, the user can go back to the first call. This is slightly different from the conference function that many smartphones have. 

Open the test menu

Code: *#7353#

How to stop it: Press the back button or home screen

Works best on: Samsung Galaxy phones

Function: On Galaxy phones only, this USSD code opens up a menu that allows the user to test some of the phones basic features. The options that can be tested are melody, vibration, speaker, dimming, camera, VT camera, Bluetooth. When each option is clicked, a shortened version of the function will open up. This is a great feature to use if a certain feature of a phone isn’t working. This feature overrides any sound or app settings that could be stopping the feature from functioning properly. It can help users determine if there is a problem with settings or if it’s a deeper problem.

A word of caution

There is no single set of USSD codes. Each of these codes triggers a response from the cell phone service provider and/or the cell tower, so each cell phone company has its own set of codes. For example, a person with Verizon service may need to type in a code that is different from a person with T-Mobile service to access the exact same function. There can also be code differences between two different types of phones within the same service provider. There are absolutely differences between the USSD codes for Apple products and Android products, but there are also different within each type of phone as well. For example, a Samsung Android and an LG Android could have different codes.

Before typing up some code found on the Internet, research the codes specific to your phone and the company that provides you with cell phone service. Be sure that you understand what the code will do to your phone and how to return the phone back to normal functioning order. In most instances, USSD codes can be stopped by simply restarting the phone.

Back in 2012, it was discovered at a tech convention that hackers can use USSD codes to install malware on phones. In this particular case, the hackers lured users into clicking on a link on a website. Once they clicked on that linked, hackers were able to remotely type a USSD code into the victim’s phone that reset it to factory settings. Always use safe Internet use practices to avoid this type of victimization. This anecdote is another example of why it’s so important to use codes from reliable sources and codes that are specific to your phone.