How do you lock your phone? Why it matters — both for security and for servicing

Locking your phone — the first line of defense for your data

A dozen or so phones pass through our shop every day. Some arrive with cracked screens, some with worn-out batteries, and some — completely unlocked. No PIN, no fingerprint, no protection of any kind. The owner hands over the phone and says: "Nah, I don't use a lock screen, it annoys me."

And then I ask myself — what if that phone had ended up in the hands of someone who isn't a trusted repair shop? Your phone holds your emails, photos, banking apps, passwords, private conversations. All of that sits behind a single swipe of a finger that takes you half a second. Or it sits behind nothing at all, if you have no lock screen.

In this article I go through every phone locking method — from the weakest to the strongest — and explain why it matters not only for your security, but for the repair itself. Because the way you lock your phone directly affects how we prepare your device for repair.

Pattern lock — popular, but far from secure

Let's start with what most Android users use — the pattern lock, that finger swipe across a grid of 9 dots. It feels intuitive, it's fast, and it gives you the sense that you've "locked" your phone. The problem is that this sense of security isn't justified.

Researchers from Lancaster University, the University of Bath and Northwest University in China demonstrated something worrying: an algorithm using a mobile phone camera from a distance of 2.5 meters can guess 87.5% of Android patterns on the first attempt. Yes, you read that right — on the first attempt. For more complex patterns (those using more dots), the success rate climbs to as much as 97.5% within the first five attempts.

How is that possible? The algorithm tracks your finger movements while you unlock the phone. It doesn't need to see the screen — it's enough to see how your hand moves. A camera 2.5 meters away is sufficient. In a checkout line, in a café, on the bus — someone behind you can record your pattern without you ever knowing.

Why are patterns so predictable?

The Android grid has 9 dots and theoretically offers around 389,112 possible combinations. But the average user doesn't use all 9 dots. Studies show that the average pattern uses only 5 dots, which cuts the number of combinations down to about 7,000. For comparison, a four-digit PIN has 10,000 combinations.

But the number of dots isn't the only problem. There are clear patterns in how people choose their pattern:

• 44% of users start from the top-left corner — that's the first dot that comes to mind, isn't it?
• 77% start from one of the four corners — a corner is a natural starting point
• Most patterns go left to right and top to bottom — we follow the same pattern as when reading text
• People choose shapes that resemble letters (L, Z, N, M) because they're easier to remember

The result? If you know these statistical patterns, you can eliminate the vast majority of possible combinations and guess someone's pattern with relatively few attempts. Android allows 5 attempts before a temporary lockout — and with a good algorithm, 5 attempts are more than enough.

Greasy smudges — the silent traitor

There's another problem people often forget: greasy smudges on the screen. When you swipe your finger along the same path hundreds of times a day, a visible trace stays on the screen. All it takes is looking at the screen at a certain angle of light and your pattern is literally drawn on the glass. This method is so reliable that researchers from the University of Pennsylvania formally documented it as a "smudge attack" back in 2010.

We see it in the shop every day. When a customer brings us a phone, we can often see the pattern on the screen before the customer even tells us. Of course, we never use that — but imagine losing your phone on the street.

PIN — better than a pattern, but with its own flaws

A four-digit PIN offers 10,000 possible combinations (from 0000 to 9999). That's more than the average 5-dot pattern, but less than what you'd think counts as "secure".

The problem with PINs is human nature. We don't choose random numbers — we choose birth dates, years, sequences that feel logical to us. And that makes us predictable.

The most common PINs — statistics that should scare you

Analysis of leaked databases shows devastating results:

• 10.7% of users use the PIN 1234 — one in every ten people
• In second place is 1111 with 6.0%
• Followed by 0000 (1.9%), 1212 (1.2%), 7777 (0.7%)
• With just 61 combinations, an attacker can guess a third of all PINs
• The top 20 most common PINs cover nearly 27% of all users

Think of it this way: if you found 100 locked phones on the street and typed only "1234" into each one, you'd unlock about 11 of them. Add "1111" and "0000" and you have almost 20 unlocked phones out of 100. With a phone that holds banking apps, email, and all your passwords — that's a terrifying statistic.

Six-digit PIN — a significant improvement

Since iOS 9, Apple has switched the default PIN from 4 to 6 digits. It sounds like a small change, but the math is dramatic: from 10,000 combinations you jump to 1,000,000 combinations. That's 100 times more possibilities.

Of course, the same rules apply here too — "123456" is the most common six-digit PIN, but the space for random combinations is incomparably larger. If you're already using a PIN, switch to 6 digits. That one extra tap dramatically increases your security.

Password — the most secure "classic" method

Both Android and iOS let you set an alphanumeric password instead of a PIN. This is by far the most secure option among the "something you know" locking methods. An 8-character password combining lowercase and uppercase letters, numbers and special characters has over 6 trillion possible combinations.

The problem? Nobody is going to type an 8-character password every time they want to check a notification. That's why a password works best in combination with biometric methods — set a strong password as your fallback, and use a fingerprint or face recognition for everyday unlocking.

Touch ID — the biometrics that changed the game

When Apple introduced Touch ID on the iPhone 5s in 2013, it was a turning point. Suddenly, locking your phone didn't require remembering anything — you just place your finger on the sensor and the phone is unlocked in under a second.

Touch ID uses a capacitive sensor that scans your fingerprint at a resolution of 500 pixels per inch. It scans the subdermal layer (not the surface of the skin), which makes it resistant to fake fingerprints made of silicone or gelatin. Every time you place your finger on the sensor, Touch ID learns and improves its model of your fingerprint.

How secure is Touch ID?

Apple states there is a 1 in 50,000 chance that someone else's finger will unlock your phone. That sounds like a small number, but let's put it in context:

• 4-digit PIN: 1 in 10,000 (if it's random)
• Touch ID: 1 in 50,000
• So Touch ID is 5 times more secure than a random PIN

But realistically, Touch ID is far more secure than a PIN in practice, because PINs are never random. When you take into account that 10.7% of people use "1234", Touch ID becomes an incomparably safer option.

What a fingerprint has and a PIN doesn't is uniqueness. Your fingerprint has between 40 and 60 measurable characteristics (minutiae) — points where ridges fork, where they end, loops, arches, whorls. Not even identical twins have identical fingerprints.

Touch ID and phone repair

Here's where this becomes relevant to us in the shop: the Touch ID sensor on an iPhone is paired with the Secure Enclave chip on the device. That means if you replace the Home button (on older models) or the Power button (on newer ones), Touch ID won't work with the new button unless Apple performs a calibration.

That's why we always recommend that customers keep their original button whenever possible. If only the screen glass is damaged and the Home button is working, we carefully transfer it to the new screen. Touch ID keeps working without any issues.

Face ID — the future arrived in 2017

With the iPhone X, Apple removed the Home button and introduced Face ID — a face recognition system that set a new industry standard. Face ID doesn't use an ordinary camera. It uses the TrueDepth system, which projects 30,000 infrared dots onto your face and creates a precise 3D map.

Why does this matter? Because an ordinary 2D photo can't fool Face ID. The system knows the difference between your real face and a photo, a mask, even a realistic 3D sculpture. The infrared dots measure depth — the distance between your nose and cheek, the shape of your eye sockets, the contour of your jaw — things that can't be replicated with a photograph.

Numbers that impress

Face ID has a 1 in 1,000,000 chance that someone else could unlock your phone with their face. That's 20 times more secure than Touch ID and 100 times more secure than a random four-digit PIN.

Face ID also adapts. If you wear glasses, grow a beard, change your hairstyle — the system learns and adjusts gradually. Apple even added mask support in iOS 15.4, using the area around the eyes for identification.

Face ID and screen replacement — this is what you need to know

This is something every user should understand before coming in for a repair: Face ID depends on the TrueDepth camera integrated into the top of the screen. When you replace the screen on an iPhone with Face ID, that camera must be transferred and calibrated properly.

Here at Viper we use Genuine Apple parts for models where they're available. Why? Because cheap aftermarket screens can break Face ID. Apple's software checks component serialization — if the screen isn't properly paired with the device, you get a warning in settings, and in the worst case Face ID stops working altogether.

With Genuine Apple screens, Face ID works without any issues after replacement. Calibration is done through Apple's diagnostic tool, and the phone behaves as if it had never been opened. That's the difference between a "cheap repair" that saves you 2,000 dinars and a quality repair that preserves the full functionality of your phone.

Optic ID — the newest generation of biometrics

With the Apple Vision Pro, Apple introduced Optic ID — an iris recognition system that is currently the most secure biometric method on the market. The iris — the colored part of the eye around the pupil — has over 200 measurable characteristics. For comparison, a fingerprint has 40-60, while the face (for Face ID) uses around 30,000 infrared dots for 3D mapping.

Why is the iris so reliable? Because it forms during the prenatal period and remains unchanged throughout your entire life. Not even identical twins have the same irises. The probability of a false match is 1 in 1,000,000, the same as Face ID, but with completely different biology as its foundation.

Optic ID uses near-infrared LED light that is invisible and safe for the eye. Scanning is instant and works even if you wear glasses or contact lenses. This is technology that will likely come to the iPhone in the coming years, perhaps in combination with Face ID for multi-layered biometric authentication.

Side-by-side comparison of all locking methods

Physical protection — just as important as digital

We've talked about digital locking, but there's another dimension of protection that people neglect: physical screen protection. Because what good is Face ID if your screen is cracked and the touchscreen doesn't respond?

In our shop we see a direct correlation: phones without a screen protector or a case come in for repair significantly more often. One drop onto concrete and the screen is done — and with it, often, the functionality of your biometrics.

That's why we recommend a hydrogel screen protector as a minimum level of protection. With us it costs 2,000 RSD with any repair — that's less than the price of one coffee a day over a month, and it protects the screen from scratches and minor impacts. Hydrogel film has a self-healing property — smaller scratches disappear on their own within 24-48 hours thanks to the elastic polyurethane material.

For maximum protection, combine a hydrogel screen protector with a quality case. That's an investment of 2,000-3,000 dinars that can prevent a 15,000-30,000 dinar repair.

How to prepare your phone for repair — a practical guide

Now we come to the part that's directly tied to our everyday work. The way you lock your phone affects how we approach the repair. Here's what you should do before you bring your phone in:

1. Back up your data

This is rule number one. Before any repair, make a backup:

• iPhone: iCloud backup (Settings → your name → iCloud → iCloud Backup) or a backup to your computer via iTunes/Finder
• Android: Google backup (Settings → System → Backup) or Samsung Cloud for Samsung devices

Why does this matter? Because even though we do everything to preserve your data, a repair means opening the phone and handling components, and there is — however small — a risk. A backup is your insurance policy.

2. Turn off Find My iPhone / Find My Device

This is critical, especially for iPhone. If Find My iPhone is turned on and the phone is linked to your Apple ID, we can't perform certain diagnostic procedures. Apple's Activation Lock prevents anyone (including repair shops) from accessing certain functions without your Apple ID and password.

Before you bring your phone in:

• Go to Settings → your name → Find My → Find My iPhone → turn it off
• You'll need your Apple ID password — remember it or write it down
• This doesn't delete your data, it only temporarily disables tracking

3. Remember your passwords

It sounds trivial, but it happens every day: a customer brings in a phone, we finish the repair, and they can't log in because they forgot their Apple ID password. Or the PIN. Or the pattern.

Before the repair, check:

• Do you know your Apple ID and password?
• Do you know the PIN/password for your lock screen?
• Do you have access to the email tied to your Apple ID (for verification)?
• Do you know your Google account and password (for Android)?

4. Let the shop know about your lock status

When you bring the phone in, tell us:

• Which type of lock you use
• Whether Find My is turned off
• Whether the phone has iCloud Lock or Google FRP (Factory Reset Protection)

If the phone is locked with iCloud Lock, we can't access diagnostics or complete the repair until the lock is removed. That's not a limitation of our shop — it's Apple's security measure designed to protect your data, and we respect it.

5. Your data is safe with us

I want to emphasize this: while you wait for a screen or battery replacement, your data is safe with us. Viper has been around for more than two decades, and our reputation is built on trust. We don't access your personal data, we don't look at your photos, we don't read your messages. The phone is used solely for diagnostics and testing after the repair.

But — and this is key — what happens when you lose your phone on the street? What happens when someone steals your bag on public transport? In that case, the only thing standing between the thief and your data is your lock screen. So please — set one up. Today. Right after reading this article.

Our recommendations for optimal locking

Based on everything we've covered, here are our recommendations ranked by priority:

For iPhone users:

1. Use Face ID or Touch ID (depending on your model) — it's the fastest and most secure way
2. Set a six-digit PIN as your fallback — avoid birth dates and obvious sequences
3. Turn on "Erase Data" — after 10 failed attempts, the phone erases itself automatically (Settings → Face ID & Passcode)
4. Turn on Find My iPhone — if you lose your phone, you can locate it or erase it remotely

For Android users:

1. Use your fingerprint if your phone has a sensor — rear, side or under-display, they all work reliably
2. Avoid pattern lock — if you're already using a pattern, make it with at least 7 dots and don't start from a corner
3. Set a six-digit PIN as an alternative — same rule: no 123456 or birth dates
4. Turn on Google Find My Device — a free service that lets you locate and remotely erase your phone

Frequently asked questions (FAQ)

Does Face ID work after a screen replacement?

Yes, but only if the replacement is done properly. Face ID depends on the TrueDepth camera, which has to be carefully transferred from the old screen to the new one and calibrated. Here at Viper we use Genuine Apple parts and Apple's diagnostic tool for calibration, so Face ID works completely normally after the replacement. Cheaper aftermarket screens can break Face ID permanently — that's one of those situations where saving a couple of thousand dinars can cost you much more.

Can a repair shop unlock a phone without the passcode?

No, and that's intentional. Neither Apple nor Google allow repair shops to bypass the lock screen. It's a security measure that protects you — the user. If you've forgotten your passcode, the only option is a factory reset, which erases all your data. That's why a backup before a repair is so important.

How do I prepare my phone for a repair?

Back up your data (iCloud or Google), turn off Find My iPhone/Find My Device, remember all your passwords (Apple ID, PIN, Google account), and let the shop know about your lock status. If you have iCloud Lock, the phone has to be unlinked before the repair — otherwise we can't access diagnostics.

Does Touch ID work with a new screen?

The Touch ID sensor is paired with the device. As long as the original button (Home or Power button, depending on the model) is properly transferred to the new screen, Touch ID will work normally. We always keep and transfer the original button unless it's physically damaged.

How secure is a 4-digit PIN really?

In theory it offers 10,000 combinations, but in practice it's much weaker. Statistics show that 10.7% of users use 1234, and with just the 61 most common combinations you can guess a third of all PINs. We recommend switching to a six-digit PIN (1,000,000 combinations) or, even better, using biometric locking with a strong PIN as a fallback.

Is face recognition on Android phones as secure as Face ID?

Usually not. Most Android phones use 2D face recognition via an ordinary front camera, which is far less secure than Apple's Face ID system with its 30,000 infrared dots and 3D mapping. A 2D system can be fooled by a photograph in some cases. The exception are premium models like the Samsung Galaxy S24 Ultra, which have more advanced depth detection, but even they don't reach the level of Face ID.

What happens if I forget my Apple ID password before a repair?

If you can't turn off Find My iPhone because you've forgotten your Apple ID password, visit iforgot.apple.com to reset the password before bringing your phone in. Without that, the phone stays locked by Activation Lock and we can't access diagnostics. This is a common problem and it's easy to solve — you just need access to the email tied to your Apple ID.

Conclusion — the half second that protects your digital life

Locking your phone isn't complicated. Face ID, Touch ID, a fingerprint — all of it takes less than a second. And that second stands between your data and anyone who gets hold of your phone.

We often get phones in the shop with no protection at all — no lock screen, no screen protector. It's like leaving your car unlocked with the key in the ignition. Yes, most of the time nothing will happen. But the day it does — you'll regret it.

Set up a lock. Use biometrics. Put a strong PIN as your fallback. And when you bring your phone in for a repair — make a backup, turn off Find My, and remember your passwords. That way you help us give you the best possible service, and you can be sure your data is protected at all times.

If you have any questions about locking your phone, preparing for a repair, or if you'd like to book a repair — get in touch. We're here for you.