How to Use the Hidden Field Test Mode on Your iPhone to Check Cellular Signal Strength

If you are experiencing dropped calls, slow internet speeds, or poor cellular reception, the standard signal bars at the top of your iPhone screen rarely tell the whole story. Those bars are an approximation and can be notoriously inaccurate. To get the true mathematical measurement of your cellular connection, you need to access a hidden diagnostic menu built into iOS called “Field Test Mode.”

Field Test Mode is designed for engineers and technicians to read the raw data coming from the iPhone’s cellular modem. However, anyone can access it by dialing a specific shortcode. This mode allows you to see your exact signal strength measured in decibels-milliwatts (dBm), providing an incredibly precise metric for troubleshooting.

This guide explains how to enter Field Test Mode and interpret your true cellular signal strength on an iPhone.

Step 1: Disable Wi-Fi

To ensure you are measuring your cellular connection and not inadvertently reading data related to Wi-Fi Calling, you must turn off Wi-Fi before entering Field Test Mode.

1. Swipe down from the top-right corner of your screen to open the Control Center.
2. Tap the blue Wi-Fi icon to turn it off (it will turn grey).
3. Ensure the cellular data icon (the antenna) remains green.

Step 2: Enter the Field Test Code

You access this hidden menu using the iPhone’s Phone app.

1. Open the Phone app on your iPhone.
2. Tap on the Keypad tab at the bottom.
3. Carefully dial the following code exactly as written: *3001#12345#*
4. Tap the green Call button.

Instead of making a phone call, your screen will instantly transition to a grey and white diagnostic dashboard labeled “Field Test” or “Dashboard.”

Step 3: Read Your Signal Strength in dBm

The layout of Field Test Mode varies slightly depending on whether your iPhone uses an Intel or Qualcomm modem, but the metric you are looking for is universally called rsrp or RSRP (Reference Signal Received Power).

1. On the main dashboard, look for a metric labeled rsrp. If you do not see it on the main screen, tap the menu icon (usually three lines) and select LTE or 5G, then look under the Serving Cell Meas (Serving Cell Measurements) section.
2. You will see a negative number next to rsrp, such as -95 or -115. This is your true signal strength in dBm.

Interpreting the dBm Number:

Because dBm is a negative number, the closer the number is to zero, the stronger the signal.

• -50 dBm to -79 dBm: Excellent signal. You are likely very close to a cell tower.
• -80 dBm to -99 dBm: Good signal. You should have no problems with calls or data.
• -100 dBm to -109 dBm: Weak signal. You may experience slow data speeds or occasional dropped calls.
• -110 dBm to -120 dBm: Very poor signal. You are on the edge of dropping the connection entirely.

How to Exit Field Test Mode

When you are finished checking your signal strength, exiting the diagnostic mode is very easy.

1. Simply swipe up from the bottom of your screen (or press the Home button on older models) to return to your home screen.
2. You can now turn your Wi-Fi back on.