Dial *3001#12345#* and press the Call button. This will launch the Field Test Mode app and where the bars/dots were in the top left corner of the screen, you'll now see a negative number. The negative number is the decibel signal strength reading and should be followed by the carrier name and then the network type.
Accessing Field Test Mode on an iPhone can be quite straightforward: simply go to your phone's dialer, type in *3001#12345#* and hit the dial button.
Open phone app and dial *3001#12345#* Tap Nr Reach Attempt under 5G to measure 5G signals. Tap Reach Attempt under LTE to measure 4G signal (RSRQ/SINR not available) RSRP value represents signal strength.
By pressing *3370# or #3370#, you'll activate your phone's “reserve battery power”. Battery life will increase by 50%. The reserve will automatically charge up the next time you change your device.
To enter Field Test mode, open the Phone app and dial *3001#12345#* on the keypad. Yes, really. We weren't kidding about this being a truly hidden trick! Hit the call button, and Field Test will start up.
*3001#12345#
This secret code allows your phone to enter a so-called 'Field Test Mode' and gives you precise data on how strong your signal strength really is. While signal bars have always given us assurance that our phone signal's just fine, the truth is, information displayed on these bars are often inaccurate.
By typing in the code *3001#12345#* you can enable the field test mode, which will show you a lot of technical data from your carrier. Other than that, you can also see how strong is the signal received by your iPhone. If you think you're having signal reception issues, you can use this to check it out!
*#9900# Opens up system dump mode.
Android code: *#*#4636#*#*
This code will open up a menu that shows information about your phone's data usages. Here's how you can retrieve deleted text messages on your iPhone.
*2767*3855# (Wipe Your Device and Reinstall Firmware)
Think of it as a factory reset—type this code on your dialer and run it, and it'll effectively delete all data from your phone, and wipe it clean.
Hide Caller ID: *31#
The caller might have hidden the ID intentionally or sometimes it can be accidental. If you want to hide the caller ID dial *31# and press call button.
When you dial *#21#, you are, in fact, activating a feature access code that quickly tells you the status of call forwarding for your phone. It's a quick way of seeing what, in the case of this particular 'setting interrogation code,' your call forwarding settings.
Call barring lets you block incoming or outgoing calls to and from your phone. This may be useful if you keep receiving unwanted telemarketer calls or want to avoid expensive international calls. To check if the feature is enabled on your device, dial *#33#. Use the code *33*pin# to enable call barring on your iPhone.
##002# - If your voice call or data call, or SMS call has been forwarded, dialling this USSD code will erase them. *#21# - By dialling this USSD code, you would get to know if your calls have been diverted somewhere else or not.
Key hardware info: *#0*#
When you enter *#0*# into the phone's dialer, the device enters service mode and brings up a diagnostics menu. From this screen, you can view and run multiple diagnostics to test device hardware like buttons, sensors, and cameras.
Battery status (ADC, RSSI reading) *#0011# Service Menu.
Code to check if phone is tapped: *#21# Code to show unknown connections and tracking (for Android): *#*#4636#*#* or *#*#197328640#*#*
It's called the System UI Tuner and it can be used for customizing an Android gadget's status bar, clock and app notification settings. Introduced in Android Marshmallow, this experimental menu is hidden but it's not difficult to find. Once you get to it, you'll wish you knew about it sooner.
For newer Android devices
Enter *# *# 72786 #* #* into the dial pad. Don't tap the call icon or try to connect.
These types of errors usually occur when a field in your submission has an invalid data entry, ie. text in a number field, the wrong number of decimal places, an incorrect date format.
Replies. 3: Redownload of iPhone-only, or iOS and tvOS app (excluding iPad-only) 3F: Redownload of Universal app (excluding tvOS) 3T: Redownload of iPad-only app.
Announcement 19 - Calling Restrictions Prohibit Dialing Beyond Your Service Area.