We often gauge network quality by looking at the signal bars displayed at the top-right corner of an iPhone screen. Four bars indicate a strong network, while one or two suggest a weak one; however, do these bars truly reflect the precise signal strength? The short answer is no.

**Signal Strength Constantly Fluctuates**
In reality, the signal bars on an iPhone provide a generalized visual representation of network strength. Actual mobile network conditions are constantly changing. Factors such as your location, surrounding buildings, network traffic, and distance from the tower all influence signal strength.

If every minor fluctuation were reflected in the bars, the signal icon on the screen would constantly jump up and down. Therefore, signal details are categorized into specific levels and displayed as bars.

This is why the number of bars displayed can differ across various phones or networks, even when the actual signal strength is identical. Consequently, it is difficult to determine the exact network power solely by looking at the signal bars.

**How ​​to Check Actual Signal Strength Using a Secret Code**
If you wish to view detailed network information on your iPhone, you can use "Field Test Mode." To do this, first turn off Wi-Fi and open the Phone app on your iPhone.

Next, type the code `*3001#12345#` into the dialer.

Then, press the call button. This will launch the iPhone's Field Test Mode, displaying various technical details regarding the network. Here, you may see values ​​such as RSRP, which indicates the actual signal strength in dBm.

dBm values ​​are negative; generally, a signal around -70 dBm is considered strong, whereas a signal around -110 dBm is considered very poor. However, the interpretation of these figures can vary depending on network technology and conditions. So, next time, instead of judging the network solely by the signal bars, use this secret iPhone code.