CAT S31 Review – Hardened to the Core


Unbeatable protection and battery life

The name CAT evokes a certain respect in the world of heavy equipment. As the world's largest construction equipment manufacturer, there's a good reason this applies. CAT's name doesn't just cover heavy construction equipment too, it also covers the gamut of items that might be found at a construction site, or in any outdoors situation in general. CAT's phones, as a result, have a rugged look and feel to them, and are built to withstand the elements without needing an extra case or pampering of any kind. The CAT S31 is the one of the latest in rugged phones from the company, and it's this phone that we'll be taking an in-depth look at today.

Video Review

Specs and What's In The Box


As the name implies, this is a minor upgrade from the CAT S30 that was released over 2 years ago, and features the same 64-bit quad-core Qualcomm Snapdragon 210 processor (1.3GHz Cortex-A7) and Adreno 304 GPU as that phone. Most of the rest of the package is a sizable upgrade though, including a 4.7-inch 16:9 720p TFT screen, 2GB of RAM and 16GB of internal storage. MicroSD cards are supported for expandable storage, and the screen is covered in Gorilla Glass 3 for excellent scratch protection. A 2-megapixel camera sits on the front, while an 8-megapixel with single LED flash can be found on the back. Three hardware buttons are found on the front for navigation: back, home and overview (multi-tasking). Android 7.1.2 Nougat powers the experience as of this writing.

The entire body of the phone is encased in a rubber shell, and is IP68 certified water and dust proof, not just resistant. MIL-STD-810G compliance means it's rated for drop-to-concrete from up to 1.8m (5.9ft) without taking significant damage, and it's also rated to be salt, dust, humidity, rain, vibration, solar radiation, transport and thermal shock resistant. The body measures in at 146mm high by 74.4mm wide and 12.6mm thick, with a healthy weight of 200g. A single nano-SIM tray can be found above the separate microSD card tray, both of which are under a sealed hatch. A 4,000mAh battery is packed inside the sealed case, recharged quickly with Qualcomm's QuickCharge 2.0 via microUSB cable. CAT sells the S31 for $329.99 unlocked on their website, or at Global Industrial, Grainger, Amazon, BestBuy, eBay, and The Home Depot.


Despite the relatively small box, CAT includes a few bonuses aside from the usual pack-ins with a phone. A 5v/1.5a wall charger and USB Type-A to microUSB cable is included, as well as a set of black earbuds for listening to music without needing to buy extras. A warranty card explains the support agreements in the US, and a small manual and SIM card will get you started.

Hardware and Display


CAT's hardware is actually manufactured by Bullitt Group, who specializes in rugged phones for other companies as well. As such you'll find an extremely high quality rugged build, as the vast majority of the case is a hard rubberized plastic and is built to withstand the elements. Being MIL-STD-810G rated is a big deal, especially with the rest of the design in tow, and means that you will not only never need to buy a case for the CAT S31, but you'll essentially never have to worry about it breaking under normal situations either. Gorilla Glass 3 on the front is far more scratch resistant than newer generations of Gorilla Glass, which means you'll likely never see a scratch on the display either.

The display on the front is fairly small, which is certainly a positive for some folks who prefer a smaller device. In outdoor situations, brightness is the most important factor for visual quality, and it's here the CAT S31 doesn't disappoint. The rest of the display is serviceable, with pixel density of 312 pixels-per-inch to make things sharp and clean. Below the display is a set of physical navigation buttons that require a good push, and in-between these buttons and the display is a front-facing sound bar. Some fairly sizable bezels are not much of a big deal on this type of device, with the earpiece, camera and CAT logo above the display. There's no fingerprint scanner on the CAT S31, which is certainly a weakness to the design and spec sheet overall.

All ports on the phone are protected behind a waterproof seal, including the 3.5mm audio jack up top, microUSB port on bottom, and SIM tray and microSD slot on the right. The button situation on the phone is unique, and a bit confusing at first. Separate volume buttons are located on the right, while the left side of the phone holds the power button and programmable burnt orange button too. This button can be assigned to any function, either as a push-to-talk (PTT) for walkie-talkie style function, or any action can be assigned to a short and long press instead. The phone lays perfectly flat on any surface, and features grooved grips around the back and sides. While 200g and 12mm sound like a thick, heavy phone, it really doesn't feel crazy while holding it. Overall it's a well balanced design that looks and feels the part.


The real negative of the phone is the touch component of the display, the digitizer. While a handy glove mode is supported for using the phone even without specialized capacitive touch gloves, the accuracy of the digitizer itself leaves a lot to be desired. I found myself constantly getting frustrated with typing on the phone, as I tend to type very quickly and the phone had a hard time keeping up. I'd often get phantom touches or double taps where I didn't press, causing me to regularly correct my words and spend an inordinate amount of time having to erase letters and characters that were seemingly randomly pressed. I didn't experience these issues when using single-point touch apps though, so if you're not a fast typer or prefer swiping instead, you'll be just fine here.

Performance and Benchmarks


Qualcomm's Snapdragon 210 is no powerhouse processor, and while it's a quad-core 1.3GHz chip, it's not fast by most modern measurements. That's not to say the phone is obnoxiously slow or anything, rather it's rather usable in most situations, but you may find yourself waiting longer for it to finish a task or load an app than other phones would. Intense processing apps and games simply won't run well here. The processor is already low power as it is, and running a 720p screen means that it's just not going to be able to keep up with these difficult tasks.

Thankfully everyday things like web browsing, chatting or social networking run just fine, albeit a bit slower than more expensive phones would deliver. This is essentially the difference between a phone that feels butter smooth, and a phone that feels just a bit choppy. At the end of the day though you'll still get the task done, and the phone is no worse for wear in many cases. Just don't expect to game much, if at all on this phone, it's just not up to that level. Benchmarks definitely reflect the slower nature of the phone, and you'll find the results fit right in with what performance on more intense apps and games belays.

Connectivity, Sound and Battery Life


CAT sells the S31 in the US officially and unlocked, and it's obvious from the get-go that this is the case. Drop just about any SIM card in the phone and you'll find a strong 4G LTE connection, even inside brick buildings, with support for higher quality Voice over LTE (VoLTE). For times when signal strength is weak, the CAT S31 supports WiFi calling out of the box, which extends calling and texting reach well beyond a cell network's abilities. Bluetooth 4.1 connects essentially all Bluetooth supported accessories, and WiFi 802.11b/g/n are supported. While you're out and about, the built-in FM tuner will come in handy for playing tunes, and tri-GPS support (A-GPS, GLONASS, BDS) will ensure you won't get lost either.


Sound coming from the front-facing speaker is rather good in general, and this is easily the best place to put any speaker on a phone. The wide soundbar leaves room for good sized speakers inside, and the volume level is loud and clean, with little to no distortion even at maximum volume. A 3.5mm audio jack supports wired audio, and just like all flaps on the phone, will alert you if it has been opened or become loose, so as to preserve the waterproof nature of the phone.

Battery life is absolutely superb, and it's doubtful that anyone will ever find the battery life on the CAT S31 to be anything less than extraordinary. Our best run was 8 hours of screen on time spread across two full days; something most phones could only dream of, let alone ever achieve. Charging is still quick too if you need it, with 10W Qualcomm QuickCharge 2.0 giving the battery a quick top-up in 30 minutes, and taking just shy of two hours to charge the battery in full.


The software side of the house is almost completely stock Android 7.1 Nougat, which is a very good thing on low power phones like this. The biggest prevailing custom feature of the S31 is the orange programmable key on the side, which can be set to any action you would like. Short press is separated from long press, and either any app can be launched via these pressed, or a set of actions (such as toggling the flashlight) can be chosen instead.  Alternatively this button can be used as a PTT (push-to-talk) button that allows the phone to act as a walkie-talkie, or an old-school Nextel if you'd prefer.

CAT doesn't pack any real bloatware on the phone, rather there's a web wrapper app that functions as a way to recommend apps that are good for hiking, construction and plenty of other related, outdoor activities and jobs. CAT also offers official support through their website, which can be easily accessed through a quick link in the app drawer. Standard Google and AOSP apps are included, with no arbitrary restrictions on swapping out stock apps as some phones will restrict.


The overall camera experience is much the same as the rest of the phone. It's a little on the slow side, and it's not the best quality in the world, but it will get the job done for the most part. Initial launching of the camera will take several seconds, but once that's been loaded, it only takes a second or two to bring back up when you want to take a shot again. The interface feels a bit dated at best, but it's easy enough to navigate. A left-hand swipe-out menu brings up the options, while a row of quick toggles across the top are available for things like toggling between front and rear cameras, or toggling HDR. Modes are found in a pop-up menu on the bottom right, with only three options: photo, video and panorama.

Picture quality is sub-par at best, with the biggest issues being focusing issues and color accuracy. Colors are often very off, with heavy green or blue tints in fluorescent or other indoor lighting. Sometimes it would do OK, especially with incandescent or natural sunlight, but this was definitely an issue in our testing. Focusing is also very slow, and there were enough times where it took too long to get a good focus before the shot was taken, leaving some shots looking a bit soft as a result.

The front-facing camera fairs better with color accuracy, but at 2-megapixels it's not going to be the highest resolution camera in the world. Video is going to be about the same as well, as the highest quality that can be recorded is 720p. In a world of cheap 4k TVs and other displays out there, 720p is pretty low resolution, and will definitely look a bit lower quality in the end. It's definitely not the best part of the experience on the phone, but it's not totally terrible either.

The Good

Rugged design

IP68 and MIL-STD-810G rated

Programmable side button

2-day battery life

Sharp, bright screen

microSD card support

3.5mm audio jack

VoLTE and Voice over WiFi

Glove mode for the screen

Front-facing speaker


The Bad

Slow performance

Expensive for the specs

Sub-par camera

Digitizer has phantom touch issues

No fingerprint scanner



There's certainly a longer list of positives here than negatives, but the negative aspects of the phone are still glaring. At just over $300 it's more than disappointing to see a phone that performs so slowly in everyday use, not to mention that multimedia and gaming don't fair well here. The lack of a fingerprint scanner makes the phone feel older than it should, and the camera experience overall just isn't great. What is good, however, are the rugged hardware features and design, as well as the battery life. A 3.5mm audio jack means you can use wired headphones without having to worry about silly adapters or keeping Bluetooth headsets charged, and support for 4G LTE, VoLTE and Voice over WiFi are certainly huge deals when it comes to basic connectivity and daily use. It's not a phone for everyone, but those that are looking for a simple rugged device that can withstand the elements may find what they're looking for.

Buy the CAT S31 at Amazon