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iPhone Test Guide Background

Field Test Mode is a hidden feature on the iPhone which allows you to see technical details of the device, including the true cell signal strength displayed as a number rather than the traditional signal bars or dots.

Between test cycles, it is helpful to enable and then disable Airplane mode to force a refresh of the signal data. This can also be accomplished by placing a phone call.

Entering Field Test Mode

1. Launch Settings > WiFi and turn WiFi Off. This enables you to see what network you're connected to (2G, 3G, 4G, LTE, etc).

2. For iOS 9.3 and above: Go into Settings > Cellular > Cellular Data Options > Enable LTE and turn LTE to Off. For iOS 9.2 and below: Go into Settings > Cellular > Enable LTE and turn LTE to Off. LTE readings can vary by carrier so to best interpret the signal strength; we ideally want signal readings from a previous generation network. You can also repeat the site survey with LTE enabled, just be sure to keep track of which readings are which.

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3. Go into the Phone app and switch to the Keypad, as you would do to dial a phone number. 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, dBm, and should be followed by the carrier name and then the network type.

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Note: If you see "‹ Back to Phone" in the top left corner. In iOS 9+, Apple updated the Field Test Mode app so that instead of showing the decibel signal strength in the top left corner, it now says "Back to Phone". To take decibel signal readings on an iOS9 or newer iPhone, follow the steps below under the heading Always show Decibels instead of Dots. When taking signal readings, move to the location where you want to take the reading, wait for 30 to 60 seconds for the signal readings to catch up, and then record the signal strength, carrier, and network type (2G, 3G, 4G, LTE, etc.). To exit and return your iPhone to normal status, all you need to do is hit the Home button. Also remember to go back into Settings and enable WiFi and Cellular LTE. This mode is available on any iPhone running iOS 4.1 and all later versions.

Always show Decibels instead of Dots

If you want your iPhone to always display numerical signal strength instead of signal bars, you can perform the following process.

1. Once in Field-test mode (accessed by entering and dialing the code above), press and hold both the power button and home button simultaneously until your iPhone powers off. Once your device powers off, release the home button while continuing to hold the power button. Your iPhone will restart. Once the smartphone has restarted, these settings will remain.

2. To exit this permanent, field-test mode, simply reboot the phone or re-load Field Test Mode and exit it via the Home button.

Turning on Airplane Mode

1. Use your finger to swipe up from the bottom edge of your screen. The quick panel will appear. Select the airplane icon to enable Airplane Mode.

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2. To enable the radios again, simply swipe up from the bottom edge of the screen and select the Airplane icon to disable Airplane Mode.