Apple’s iOS is renowned for being an intuitive and transparent operating system, but it’s not without its little secrets. Take the hidden Field Test mode, for instance, which could help you get to the bottom of those signal black spots.

What is Field Test mode?

Field Test mode is a hidden screen within that breaks down the status of your local cellular signal, amongst other things. It’s hidden because it’s intended for use by engineers and technicians first and foremost, not the general public.

Sure enough, while you can access Field Test mode yourself (we’ll show you how in just a moment), the information it provides will most likely go over your head. We’re talking about a highly technical breakdown of the various elements that go into connecting you to your nearest cellular base station.

Why access Field Test?

As we’ve mentioned already, Field Test isn’t strictly intended to be used by your average iPhone user, harmless as it is to do so. But there are a couple of potentially useful pieces of information buried in there.

Most notably, it’s possible to get a precise numerical reading of your current cellular signal. Typically you only get a vague four–bar indicator at the top of your iPhone display, which doesn’t really spell out the strength of your signal with any precision.

Field Test will also let you find out precisely where the signal is at its strongest in your home, which can be very useful information if you often struggle to maintain a decent connection around the house.

Using Field Test is a great way to tell for sure that you’re getting a flat out bad signal, and to ascertain whether obtaining a cell phone signal booster might be a good idea.

How do I access Field Test?

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. It might take a few seconds to supply the initial cellular snapshot.

How do I find out my signal strength?

Just enter Field Test mode, tap the right–hand tab at the top, and select Serving Cell Meas under the LTE heading.

The figures marked rsrp0 and rspr1 represent your current cellular signal in decibel milliwatts (dBm). Don’t worry, they’re supposed to be negative numbers.

The lower the figure, or more specifically the closer to –40, the stronger your signal. The higher the figure, or the closer to –130, the weaker your signal. Use this seemingly arcane knowledge to search for hotspots of good and bad connectivity wherever you may be, Enjoy!