Roughly 77 percent of Americans use a smartphone, according to a Pew survey, but phones still hide secrets that most people might not know about. Most smartphones have hidden functions that you can access by punching in specific strings of numbers and symbols. These “backdoors” gives you access to features that, for the most part, you will probably never need to use, but they can occasionally come in handy — and besides, cheat codes are always fun.

We’ve rounded up some of the more practical codes for both Android and iOS devices. To use them, open your phone’s dialer and type in them (depending on your phone’s make and model, you may also need to hit the call button).

Note that these codes may not work on every device; some service providers go so far as to disable most hidden codes on their phones. In addition, there is another type of code called a USSD (Unstructured Supplementary Service Data), which send a signal to your service provider when you input it; these codes are used for things like checking your data usage.

One warning: While some of these hidden codes are benign, others do things like factory reset your phone, so be careful not to input codes on a whim.