Did you know that your smartphone had hidden menus?21
What code, you ask? Well, you've probably heard of *#06# which you type in your dialer, as if you were about to "call" it. When this particular code is entered, and it should work on any cell phone, the device's identity number (IMEI) is displayed. A smartphone's hidden menu can be accessed with a code that looks pretty similar to this one.
On iPhone, for example, you enter *3001#12345#* in the Phone app and then hit the call button to get to the field test menu. There's not much going on there, however, unless you're a technician. You can view SIM card information, details on the cell network's status, and all sorts of other cryptic numbers. It is interesting that signal strength in displayed in decibels while in this menu, not represented by circles.
Hidden menus and codes on Android phones may differ, depending on the device's make and model. This one, however, should work on most – *#*#4636#*#* (or *#*#INFO#*#*). It takes the user to a testing menu where network information is displayed, along with details on battery status and app activity. Be warned: don't change anything and don't press any buttons in this menu unless you know what they do! On a side note, this particular menu was used to "enable" 4G LTE in Canada on the Nexus 4.