The vivo X21 is among the first (well, actually the second, after the vivo X20 UD) smartphones to feature an in-display fingerprint sensor, which should function in this manner when it does work:-
The sensor is made by Goodix, a Shenzhen-based outfit which also supplies conventional fingerprint sensors and touch panels to Huawei, Xiaomi, Nokia and a whole host of other brands.
As far as we can tell, the technology works not in a capacitive manner as standard fingerprint sensors do, but by capturing reflected light between the OLED pixels (it only works with OLED displays for this reason, as LCD displays would have a backlight layer.) Goodix claims that its in-display sensor has a 2% false rejection rate, and works faster than capacitive sensors.
Unfortunately, at least in the vivo X21, we found that these claims didn’t seem to hold water…
First off, in case you were wondering, this is an in-display fingerprint sensor, not a display-wide fingerprint sensor. The phone will indicate on the display, with an animated fingerprint icon, exactly where the screen must be touched (or rather, pressed - more on this later) to unlock it. If the display is off, the icon will appear only when the X21 is moved or picked up, which can actually be hugely annoying: if you’re driving, the phone will be snugly ensconced in a car mount, and what then? You’ll have to resort to pressing the power button to bring up the icon, whereas phones with conventional fingerprint sensors will unlock immediately the moment their sensors are touched.
Now, all of this might be forgivable, especially that screen-off issue, if the sensor itself was fast and reliable. Here’s the bad news: it’s emphatically not.
To begin with, the unlock process - when it works - is far from lightning-fast, as on a OnePlus or Huawei device; the sensor takes something like a second and a half to recognize a finger - that is, when it wants to. In the time we spent with the phone, it was very safe to say that we ran out of tries and had to enter the unlock PIN way more times than we got a fingerprint to unlock it. In fact, it’s also safe to say that we entered the PIN more times on the vivo X21 than on all our previous phones (with conventional fingerprint sensors) combined.
In a futile week of tests, we enrolled and tried all the fingers we had, tested wet and dry fingers, sweaty palms and all, and even tried to pin down whether high ambient light levels and/or low display brightness would cause unlock failure (the phone appears to mitigate this by illuminating the touch zone in bright cyan, no matter what the display brightness is set to.) The sensor appears to be sensitive to dirt - this writer pressed it to his oily face a few times to test this, and the result was complete failure to unlock until the screen was cleaned. Indeed, it appears to be so finicky that vivo even warns that third-party screen protectors may interfere with its operation.
Certainly, having the sensor in the display saves space, and vivo deserves credit for jumping into the game of 'Innovations That Are Not Gimmicks', but as it stands, we’re not sure this technology is really ready for prime time. If the X21 is on your shopping list, you should actually test out the sensor for yourself on vivo’s in-store display phones, and be at least prepared for an experience similar to ours in real-world usage.
We’ve covered Funtouch OS in our vivo V7+ review, and the X21 serves up more of the same. In this case, it’s based on Android 8.1 Oreo, which thankfully brings one major change: notifications are coalesced in the notification shade, hurrah!
But no, there are still no quick settings in the notification shade…
Any hope that Oreo would have thrown some cookies to owners of newer vivo phones crumbled as we leafed through the pages:
It’s all there: the Chinglish and half-completed text strings, the same mix of loud and excruciatingly detailed alternating lock screen wallpapers, those skeuomorphic icons, and the inexplicable choice of bloatware (because paying for an X21 would leave me change out of S$800 for an ofo ride home?)
We think that vivo doesn’t need to ape Samsung or Huawei. But we also said in the V7+ review that that phone would have been better served with a stock build of Android, which would immediately have helped its high-powered cameras overshadow its weak processor. Likewise, the X21 could be really, really great with Android One. Think about it, vivo.
Finally, it's worth noting that the X21 doesn't have an NFC chip, which is a major surprise for a phone that costs S$799. That means you won't be able to use it for any mobile payment apps like Google Pay and the amazing number of contactless payment options available these days. What a pity.