Keypad Lock Code Entropy Calculator

Estimate valid PIN combinations, entropy bits, blacklist effects, guess probability, and lockout timing for owner-side keypad lock planning without exposing bypass steps.

🎯 Defensive presets

⚙ Code space and lockout inputs

Digit or key choices Use 10 for 0-9, 11 or 12 if the lock also accepts extra keypad keys.

Code length Longer codes usually add more entropy than pattern restrictions.

Repeat rule If no digit can be reused, length must not exceed available key choices.

Blocked valid codes Count common PINs, owner names, repeated patterns, date-based codes, and other disallowed entries.

Sequential or keypad-pattern codes blocked Enter the number of specific patterns your lock policy rejects.

Known household exclusions Optional owner-side exclusions, such as addresses, years, birthdays, or shared old codes.

Attempts before lockout This is the number of wrong entries allowed before the cooldown starts.

Lockout cooldown (seconds) Use 0 only when modeling a keypad with no enforced cooldown.

Seconds per manual entry Includes typing, waiting for response, and the next ready state.

Owner alert after attempts Useful for comparing lockout timing to notification thresholds.

Risk window to check (hours) The calculator estimates how many guesses fit inside this lockout-limited window.

Active valid user codes Multiple active codes increase the chance that one random guess is valid.

Threat model view

Online keypad mode applies lockout timing. Code-space only reports combinations and entropy without timing assumptions.

Entropy result

Valid combinations 0 accepted code space

Entropy bits 0 log2(valid combinations)

Single-try odds 0% for active valid codes

Window exposure 0% lockout-limited guessing window

📊 Current configuration summary

10^6Base formula

320Blocked codes

0/hrAllowed guesses

0 minAlert timing

📐 Entropy and formula reference

Rule	Combination formula	Example	Owner-side use
Repeats allowed	choices^length	10^6 = 1,000,000	Most flexible and easiest to explain.
No adjacent repeats	choices x (choices - 1)^(length - 1)	10 x 9^5 = 590,490	Blocks codes like 1007 and 5772.
No digit reused	choices! / (choices - length)!	10P6 = 151,200	Can reduce space sharply for long PINs.
Blacklist adjustment	valid base - blocked accepted codes	1,000,000 - 500	Removes known weak or personal codes.
Entropy bits	log2(valid combinations)	log2(1,000,000) = 19.93	Compares code spaces on the same scale.

PIN setup	Valid combinations	Entropy bits	Note
4 digits, repeats allowed	10,000	13.29	Convenient but small code space.
5 digits, repeats allowed	100,000	16.61	Ten times a 4-digit PIN.
6 digits, repeats allowed	1,000,000	19.93	Common stronger keypad baseline.
6 digits, no repeats	151,200	17.21	Rule is memorable but reduces space.
8 digits, repeats allowed	100,000,000	26.58	Much stronger when users can remember it.

⏱ Lockout timing reference

Attempts	Cooldown	Entry time	Allowed guesses per hour
5	30 sec	4 sec	360 guesses/hr
5	120 sec	4 sec	129 guesses/hr
3	300 sec	4 sec	34 guesses/hr
10	300 sec	4 sec	106 guesses/hr
3	900 sec	4 sec	12 guesses/hr

Result band	Entropy bits	Code-space meaning	Planning note
Very small	Under 14	About 4 decimal digits	Use longer codes and lockouts.
Basic	14 to 18	5 digits or restricted 6	Blacklist obvious patterns.
Good	18 to 24	6 to 7 digits	Strong for many home keypads.
Strong	24 to 30	8 to 9 digits	Good for admin or high-risk doors.
Very strong	30+	10+ digits or larger key set	Check usability and recovery process.

Lockout timing estimates are for legitimate owner-side risk planning. They do not model device flaws, credential theft, social engineering, physical access methods, or any bypass technique.

🛡 Safe configuration notes

Prefer length: Moving from 4 to 6 decimal digits changes the raw space from 10,000 to 1,000,000 codes, adding about 6.64 bits.

Blacklist carefully: Blocking personal dates and obvious sequences helps, but a huge blacklist can also make acceptable codes harder for residents to choose.

Limit active codes: Every active user, guest, or service code is another valid target inside the same code space, so remove stale entries promptly.

Use lockouts and alerts: Cooldowns, owner notifications, and audit logs reduce online guessing exposure without relying only on PIN entropy.

After plugging in your lockout settings and PIN length, the calculator does math for you. No need to compute permutation formulas or logarithms on your own.

What it tells you is that even with a standard four digit code, you’re only getting roughly thirteen bits of entropy. That’s a fancy way of saying it has ten thousand possible combinations. At a rate of guessing one code every few seconds, an attacker could theoreticaly try them all within an afternoon (without triggering any alarms). It is not much of a barrier.

How to Make Your Smart Lock Safe

Switching to a six digit code completely change the game. With just this simple jump, you add nearly seven bits of randomness, which increases the space by a factor of one hundred. The time to crack it transition from a casual afternoon project to a multi-day commitment if they’re doing it manually.

Instead of using long codes, many people attempt to offset that risk by restricting patterns or nearby keys. If I block 1-2-3-4, they reason, that will make my code more difficult to guess! Wrong. Diagonal swipes are just a small part of the overall space. Banning them removes a few percentages, cutting off a couple of points but doing little to reduce expected value of the overall attack.

Only length matter as a viable knob. Mathematically speaking, a code with no restrictions and a longer length is better than any code with a shorter length and complicated ban rules. When you pit a six digit, unrestricted code against a five digit, restricted one in tool, the former wins; again and again.

But just as importantly: What does your lock do if it makes a mistake? The calculator takes both cooldowns and attempt limits into account. These factors shifts the entire threat model from “code cracker” to “waiter. Does your smart lock start locking you out after five bad tries? Now we’re in the realm of the waiting game for attackers.

Does it have a two minute cooldown? An intruder can enter maybe fifteen code an hour. Glacially slow by computer standards, sure, but that’s all it takes to be effective at thwarting physical break-in, where stealth matters. The page has a timing reference table that shows just how much a small lockout duration cut down the number of guesses an attacker have in a given day. Good hardware design will protect you here; no amount of clever coding habit ever could of.

Intuition also fails us in other ways, such as blacklisting: many systems will automaticly reject certain types of passwords, like sequential numbers or dates (e.g., birthdays or anniversaries). That means that the list of potential “safe” choices for your loved ones to select from has been reduced, but so has the number of possible combinations overall. Even worse, if an attacker knows about your blacklist, he’s already ahead of the game. He doesn’t have to guess at a number like 1990; it is already ruled out.

The entropy calculation accounts for these restrictions and provides a practical estimate for how much searching remain. Don’t use blacklists to protect your door. Only use them to keep family members away from setting obvious passwords.

So what makes a good smart lock? At its heart, smart locks is a balance between ease of use and reasonable resistance. Something too hard to get into won’t be used, but something too easy will get picked by an opportunist. A six digit pin with a stern lockout policy is normaly a happy medium for home users: not so long that you need photographic memories in every household member, but long enough to make guesswork impractical.

Finally, your keypad isn’t a vault. It’s a friction point. It slows things down making it difficult for unauthorized people to get in, but also noticeable enough when they do. Knowing how many combinations are sitting behind those plastic buttons gives you the opportunity to set rules that keep you safe without losing convenience.

Because that quiet click at the door should stay that way. It is a minor annoyance, easily dismissed as you continue with your dinner.