The only good thing that side-mounted fingerprint scanners have going for them is that they are affordable and so allow manufacturers to include a fingerprint reader in entry-level smartphones. That aside, side-mounted fingerprint scanners are a terrible idea and need to go away as fast as possible.
Side-mounted fingerprint scanners are a type of biometric security feature that are embedded in the power button of some smartphones. To unlock the device, you have to place your thumb or other finger on the power button.
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Side-mounted fingerprint scanners deliver poor usability
How many times have you held your smartphone in your hand and your thumb naturally rested on the edge of your phone? Never; right? Hovering over the screen is the natural position of our thumb when holding a phone, which is just perfect for in-display or under-display fingerprint scanners. Where your phone has a side-mounted scanner, every time you need to unlock it or unlock an app, your thumb has to leave its natural position on the screen and travel to the edge to do so. If you have to do that often, it gets tiring.
For example, if you have app lock enabled on your smartphone for a number of apps, each time you switch to that app, your thumb has to do that travelling to the side or edge where your phone’s power button is located. Every single time. If you have done that 10 times in 30 minutes, you already know how tedious it is. If you have to do it 30 times in 30 minutes….
Side-mounted fingerprint scanners inadvertantly do unintended things
Besides the issue of natural placement, as my buddy Muyiwa reiterated, side-mounted fingerprint scanners have a habit of inadvertently unlocking your phone when you either simply want to adjust it in your pocket, or check time/notifications without unlocking the phone. I know it, too, from experience. It is so annoying.
Not user-friendly for left-handed folks
Side-mounted fingerprint scanners tend to not be convenient for left-handed users or users who switch hands frequently, as they may have to adjust their grip or use a different finger to unlock the phone. In contrast, an in-display or rear scanner does not discriminate against whatever hand you are more comfortable using.
Side-mounted fingerprint scanners have a smaller surface area
Generally, side-mounted readers have a smaller surface area than in-display and rear-mounted readers. In day-to-day use, this often results in a reduction of the accuracy and security of the scan. Even when registering your fingerprint using a side-mounted scanner, you tend to need to do repeated imprints to have your fingerprint properly registered.
Am I saying that side-mounted fingerprint scanners are useless? Of course, they are not. They serve a purpose. Like I already pointed out, they are great for entry-level devices, because they are better than not having one at all. Personally, though, for entry-level phones, I would rather the scanner is on the back than on the side.
But smartphone companies have decided that they need the back area for bigger camera modules and other features, so that is likely wishful thinking. Budget smartphone will likely have make do with side-mointed fingerprint scanners for a long time. What I do not get is why anyone should have to out up with them on more premium devices.
Why do foldable phones have side-mounted fingerprint scanners and not in-display scanners?
Why are there side-mounted scanners on premium, high-end phones? This is prevalent among foldable phones, to be more specific.
First, side-mounted scanners allow for folding phones to be unlocked in both closed and open states. A foldable phone would need two in-display scanners for that. The Vivo. X Fold2, with its dual under-display scanners, is an example of this. But this is an outlier; most manufacturers generally go with a side fingerprint scanner on their foldable devices.
Secondly, side-mounted scanners are generally more cost effective to implement. They are mature technology, compared to in-display scanners. As the prices of foldable phones drop, I expect that more manufacturers will also drop the side scanner arrangement.
The early days of in-display scanners were problematic. As with most new technology, it had its fair share of issues, including reliability issues. But those days are past now and in-display scanners have proven themselves to be as secure, as fast, and as reliable as older types of scanners. And they are perfect for usability because the scanner spot is right where your thumb naturally hovers over your phone screen.
Hopefully, side-mounted fingerprint scanners will disappear completely one day and in-display scanners, especially the ultrasonic type, rule the smartphone world. Or we might have to embrace something new entirely.