![Field Test Mode for iPhones and Android [Updated for 2026]](http://www.ubersignal.com/cdn/shop/articles/Field_Test_Mode_6f601040-a802-49bd-9467-7d387711ec6b.jpg?v=1783022684&width=1600)
When deciding on a signal booster for your space, there's one question that matters more than any other: how strong is the cell signal outside?
Your phone's bars won't answer that well, because a bar is just a rough approximation that blends signal strength, signal quality, and network noise together to give you a single reading. To make things worse, no two phone makers calculate bars the same way, so the very same spot can read three bars on one phone and full bars on another.
The good news is that your phone already knows the real numbers, and reaching them takes nothing more than a hidden screen called Field Test Mode, the same one our engineers pull up during a site survey.
What Is Field Test Mode?
Field Test Mode is a hidden screen built into iPhones and Android phones, and it shows you exactly what your phone's radio is picking up from the tower: how strong the signal is, how clean it is, and how well it holds up against the surrounding noise. Those are the same three numbers a technician leans on to decide where an antenna should go and how much of a boost a building needs.
The best part is that you don't need an app or any special gear to see them, since the screen already ships on the phone; the only trick is knowing which numbers matter and how to read them, and that's exactly what the rest of this guide walks you through.
Why the Numbers Matter More Than the Bars
Field Test Mode gives you three numbers, and each one describes a different piece of the picture.
- RSRP is your signal strength, the raw power reaching your phone from the tower, measured in dBm. It's always a negative number, and the closer it sits to zero, the stronger you are, so -80 dBm is a nice strong signal while -110 dBm is a weak one. When RSRP is low, that's the classic case a booster or DAS is built to fix.
- SINR is your signal clarity, measured in dB, and it tells you how far your signal rises above the interference and noise around it, so higher is better. It's the best predictor of real speed, and it's usually what's to blame when you've got plenty of bars but everything still crawls. Just know that on an iPhone this reading is hit or miss, which we'll come back to in a minute.
- RSRQ tells you how congested the network is, also in dB, and it tends to sag as more people pile onto the same tower, so closer to zero is better.
Put the three together and you can see what you're really dealing with. A weak but otherwise healthy signal, low RSRP with a decent RSRQ, is the classic case for a booster: the signal is out there, just too weak to make it indoors. A strong signal that's still slow is usually interference or a tower that's simply overloaded, and neither of those is something a booster can fix. And a weak signal that's also degraded, low RSRP paired with low RSRQ, is the edge-of-coverage case, where a booster can still help as long as there's signal outside to work with. Figuring out which of the three you've got is the whole reason we take a reading before we design anything.
How to Open Field Test Mode on iPhone (iOS 18 and Later)
Good news if you're on an iPhone: on current iOS (that's iOS 18 and later, including iOS 26), Field Test Mode has been cleaned up a lot, and it now shows your signal live as you move around.
- Open the Phone app and go to the Keypad. If you use Wi-Fi Calling, flip Wi-Fi off first, just so you know you're reading the cellular side.
- Dial *3001#12345#* and tap the green call button.
- The Dashboard opens right away, with your carrier info up top and your signal metrics just below; to see the full set, tap into the LTE or 5G row.
The one number to trust here is RSRP. The iPhone's SINR reading is hit or miss, it'll often show a placeholder until the modem catches up, and on 5G it may not appear at all, so lean on RSRP and RSRQ for a dependable read. It's also worth knowing that no third-party app can pull true dBm out of an iPhone, since Apple blocks it, which makes Field Test Mode the only way to see these numbers at all. When you're done, just swipe up from the bottom of the screen to exit.
How to Open Field Test Mode on Android
Android is more of a mixed bag than iOS, but the best way to check your numbers on any Android phone is a free app, so that's where we'd start. The built-in codes and menus can work too, but they vary by manufacturer and often hold back the numbers you actually want, so we've put those afterward.
The Best Way: A Signal App
An app gives you the most complete, accurate read you can get on Android: it works no matter who made your phone, and it hands you the full set, RSRP, RSRQ, and SINR, that the built-in tools often hold back. The manufacturer codes get blocked (Samsung especially), carrier-locked models lock them down, and even the settings path only shows RSRP, not RSRQ or SINR. A good app sidesteps all of it:
- NetMonster is the best all-around pick. It reads RSRP, RSRQ, and SINR on both 4G and 5G, and it'll even tell you whether you're on true standalone 5G or the 4G-backed kind.
- Network Cell Info Lite is the more visual one, with gauges and signal-over-time graphs that make it great for walking a building and mapping where the signal is strongest.
- CellMapper is worth adding when you want to know exactly which tower you're hitting, which helps a lot when you're aiming an outside antenna.
All three are free and pull the numbers straight from the radio.
Samsung Galaxy Field Test Mode
If you'd rather use the built-in tools and you're on a Samsung, dial *#0011# in the Phone app to launch Service Mode, which lays out RSRP, RSRQ, SINR, the band you're on, and the frequency all at once. There's one catch on the recent Galaxy phones, though: you'll need to switch off Auto Blocker first, which lives under Settings, then Security and privacy, then Auto Blocker, and even then a few carrier-locked models still won't run the code. That older all-purpose code you may have seen floating around, *#*#4636#*#*, has been blocked on newer Samsung phones, so it isn't one to rely on here.
Pixel and Stock Android
On a Pixel or another stock Android phone, the quickest built-in read is tucked in your settings: on a Pixel it's Settings, then About phone, then SIM status; Samsung buries it a bit deeper under Settings, then About phone, then Status information, then SIM card status; and on a OnePlus you'll find it at Settings, then About phone (or About device on some models), then Status, then SIM status. Wherever it lives, Signal strength shows up in dBm, and that's your RSRP, though you won't get RSRQ or SINR this way. That old *#*#4636#*#* code usually still works on a Google Pixel too, though it can vary by Android version, and Samsung has blocked it on newer Galaxy phones, so don't count on it unless you've got a Pixel.
How to Run a Signal Survey
Once you're in Field Test Mode, you can run a proper little site survey, the same kind of walk-through we do before designing a system, with a simple goal: find out where the signal is strong, where it drops off, and where the best home for an outside antenna would be.
- Walk the whole building, inside and out. Take a reading in each area, give each number a second to settle before you write it down, and jot down the RSRP everywhere, along with the RSRQ and SINR wherever your phone will show them.
- Hit all the key spots. Check every side of the building, north, south, east, and west, then head up to the roof or any upper floors, and finish in the rooms and work areas where people actually need their phones to work.
- Take a few readings at each spot and average them. Any single reading can be a fluke, so a handful gives you a number you can trust, and wherever the outside signal is strongest is usually where the outdoor antenna wants to go.
For a facilities or IT team, this little survey is really where the whole project begins, because it tells us whether there's enough signal outside to work with, and honestly, it's the first thing our design team asks for when we scope a building.
How to Read Your dBm (RSRP, RSRQ, SINR)
All right, now that you've got your numbers, here's what they mean, starting with RSRP, since signal strength drives most of the decision.
| Rating | RSRP (dBm) | SINR (dB) | RSRQ (dB) |
|---|---|---|---|
| Excellent | -80 or better | above 10 | -10 or better |
| Good | -80 to -90 | 5 to 10 | -10 to -15 |
| Fair | -90 to -100 | 0 to 5 | -15 to -20 |
| Poor | -100 to -110 | below 0 | below -20 |
| Very weak | below -110 |
One thing that trips people up is that this scale is logarithmic, so every 10 dB is a tenfold change in power, which is why a move from -100 to -90 dBm is a genuinely big jump rather than a small one. Treat the ranges as friendly guidelines rather than hard lines in the sand, too, since the exact cutoffs shift a little depending on who you ask and which carrier you're on.
If your RSRP lands in the Excellent or Good range, you're in good shape: the outside signal is healthy, and a booster has plenty to work with. Down in the Poor or Very weak range, you're looking at exactly the buildings we get called out to, where the signal is out there but the walls are keeping it from getting in. And if your strength looks fine but everything still crawls, that's usually interference or a tower that's simply overloaded, which is the one situation more hardware on your end can't really fix.
One last thing to keep in mind: Field Test Mode only reads whichever carrier is in your phone at the time, so if a building has people on more than one, you'll want to test each carrier with its own SIM. When we design a system that has to cover Verizon, AT&T, and T-Mobile all at once, we build it around the weakest of the three, so it pays to measure every one.
What If a Code Doesn't Work?
If a code doesn't pull up the menu, don't panic, because there are a few usual suspects worth checking before you blame the phone. On a Samsung, it's almost always Auto Blocker, so switch it off in Settings and try *#0011# again. On other Android phones, the manufacturer may have locked down that generic *#*#4636#*#* menu, in which case a free app like NetMonster or Network Cell Info Lite will read the same numbers for you. On an iPhone, just make sure you dialed *3001#12345#* exactly, and the Dashboard should open on its own.
And if you simply can't get a clean set of numbers on your own, that's a perfectly normal place to hand it off, since our team reads these every single day, and a quick call or an on-site visit will get you the same data we'd design from anyway.
How to Improve Your Signal
Once you've got real numbers in hand, the decision gets a lot easier: if your RSRP is weak inside the building, it almost always means the signal is out there but the construction is blocking it from getting in, and the answer is a professionally designed booster or DAS that captures that outside signal, amplifies it, and rebroadcasts it right where your people work. Better still, the survey you just did already tells us most of what we need, from where the outdoor antenna should go to how much of the building needs coverage.
For a small office or a single suite, one well-placed booster will often cover the whole space, but once you get into bigger footprints, multiple floors, or metal buildings that fight the signal at every wall, you're usually looking at commercial-grade boosters or a passive DAS with antennas spread throughout. We carry weBoost, SureCall, Cel-Fi, and WilsonPro, and which one we recommend comes down to what your building actually needs, not what carries the best margin for us.
If your readings come back only borderline, though, you might not need hardware at all just yet, because a few tweaks to placement and settings can sometimes rescue a weak signal on their own, and that's worth trying before you spend a dime.
Next Steps
If your numbers came back weak and you want a straight answer for your building, we're happy to put together a free system design built around your survey readings, so just call us at (800) 590-3564, and an engineer will walk you through what your readings mean, what your building needs, and the right way to solve it.
And if you're earlier in the process and just want a nudge in the right direction, our product quiz asks a few quick questions about your space and helps you zero in on the right kind of solution in a couple of minutes.