April 15, 2010 6:33 AM   Subscribe

[lock filter] Tonight I found out that the key that works in all of my house locks also works in my friend's front door. Is this common?

Despite both getting advice to the contrary, neither of us changed our locks upon purchasing the homes.

Things that may or may not matter:
We bought our houses within 2 months of each other from the same real estate agent. Both were foreclosures, but I don't think from the same bank. We are not in the same neighborhood.

Obviously we are both now going to re-key our locks, I am just curious about how this may have happened. Is it common or an amazing coincidence?
Anonymous because it's better to be safe than sorry.
posted by anonymous to Home & Garden (23 answers total) 4 users marked this as a favorite
I've had this happen to me in a rental.

We were on the top floor of a four-story building (first floor commercial, three stories of a single apartment each) in Jersey City and our key also opened the door of the neighbor on the third floor. We never tried the remaining door, but I wouldn't be surprised if the same key fit it too. We found out the hard way that the building owner had taken some other shortcuts.
posted by immlass at 6:39 AM on April 15, 2010

A co-worker of mine once told me a story of how (and im gonna mess up the details but basically) one of her friends found out this guy she had just met had a key that unlocked her front door or vice versa. My co-worker was saying this is a "sign" or some supernatural thing.

At the time, I argued that there is some more rational reason, like cost cutting from the lock company (is it the same brand of lock?) or, in your case, cost cutting at the bank (I'm sure they'd rather one master key for all their foreclosures instead of a massive key ring).

I have no facts or firm evidence to back this up, but given your report I'm going to put that as an anecdotal point in my favor that my gut reaction was right and there is some logical explanation. That or god needs to a more original shtick to communicate with us in this technological age.
posted by DetonatedManiac at 6:40 AM on April 15, 2010

If you go to Home Depot or wherever and look at their door knob selection, you will see that they are coded. It's a number on the package that indicates what key/lock set it uses. This is so you can buy two different door knobs that use the same key, or knob & deadbolt combination, what-have-you. Just make sure that both items you pick up have the same code, and you're set.

So it's probably just random chance that both you and your friend had previous owners who happened to pick out the same knob at one time or another. I wouldn't worry and change your locks unnecessarily. Unless one of you suspects that your home has been entered when you weren't there, of course. But otherwise, consider it a convenience that if you one of you goes on vacation, the other can house sit without having to exchange keys!
posted by wwartorff at 6:49 AM on April 15, 2010 [1 favorite]

Before I replaced them, some worn-out locks on my house could be opened by just about any key, including ones that were not even the same size as the correct key.

Compare your key with your friend's. Are they the same shape, e.g. the height of all the cuts is the same? If so, then you've somehow ended up with identically-keyed locks. But if your keys are different, likely your friend's front door lock is worn or sticky, to the point where incorrect keys will open it.
posted by FishBike at 6:50 AM on April 15, 2010 [1 favorite]

I had a 1970 VW Beetle. My friend had a 1964 VW Beetle. His car key fit my car's door and ignition, but my car key did not fit his car door and ignition.

I can't tell you how many times I forgot where I'd parked my car.
posted by notyou at 6:54 AM on April 15, 2010 [2 favorites]

Minor derail - how many lock options are there at Home Depot? Could a burgler just buy the lot and have access to a fair percentage of homes?
posted by amicamentis at 6:58 AM on April 15, 2010 [3 favorites]

My 1970 Impala has two keys - one for the doors and ignition, and the "valet" key for the trunk and glovebox. In 1997he glovebox lock broke, so I ordered a new set of keyed-alike locks for the glovebox and trunk from an aftermarket retailer (you purchased them in a set so they'd still be keyed together). Upon installation, I forgot to swap out the keys to the new ones, and absentmindedly opened the trunk with the old key about five times before I realized what was going on.

So it's not the exact same thing, but another example of it not being too uncommon.
posted by notsnot at 7:01 AM on April 15, 2010

It's not uncommon for cars. When I worked at a hotel, the valet brought around a VW car to the front for the guest. The guest drove off but came back 5 minutes and said this was definitely not their car because things were off (mirror, seat, radio) and the license plates were from a different state. Two different guests had the same make and color and same key.

Also, is it possible that since the properties were both foreclosures, the buyer bought/installed the same locks in an effort to keep one key for both properties?
posted by alice ayres at 7:10 AM on April 15, 2010

*I mean, since they were both foreclosures, maybe there was one buyer who bought/installed the same locks. It might have been easier for the real estate agent to keep track of the houses, as well. Just a thought.
posted by alice ayres at 7:13 AM on April 15, 2010

wwartoff has it. We bought new locksets from Home Depot a few months ago and to have them keyed alike you just have to match the lot numbers.
posted by electroboy at 7:18 AM on April 15, 2010

The average house key has five to six pins; I can't find any info on how many different depths each pin can be set at but from looking at my own keys I'm guessing 4.

So for any two locks from the same manufacturer, there's either a 1 in 1024 chance (for a five-pin lock) or a 1 in 4096 chance (for a six-pin) of the keys randomly happening to match. So, no, not that uncommon at all.

Don't bother rekeying; there are hundreds or thousands of other houses in your town that your key will fit, and always will be.
posted by ook at 7:44 AM on April 15, 2010

I doubt it's random luck — when my mom was the managing agent for a bunch of buildings here in NYC, she used to have the locksmith key all their front doors the same, so she just needed to carry one key rather than 13. I'm sure real-estate agents who have to show a lot of houses often do the same thing.
posted by nicwolff at 7:48 AM on April 15, 2010

I'm wrong. Turns out there can be up to ten depths, but the math is complicated by the fact that for mechanical reasons any adjacent pins have to be within a certain depth of each other, which rules out a lot of possible combinations.
posted by ook at 7:58 AM on April 15, 2010

Locksmith here....

Is your house a 'track' home? or Was is mass developed by the same developer? Sometimes what happens is the developers get lazy or careless and key several of the houses in the track with the same bitting.

Another thing I have seen is that homeowners will bring their door locks in, and when we take them apart we find that the lock was keyed to a master key. Of course, I always alert the homeowner of this and repair the lock so that the master key no longer will operate the lock. If the master key system was poorly designed, sometimes two different "change keys" (non master keys) will operate different locks.

I would also be interested to know if your keys are identical or just similiar in bitting. Is there much wear on either of your keys? If there is, this could indicate that while your two locks might not be identical, one of your keys has become so worn that it is actually a new key and will operate a different lock.

All of this is conjecture, and without seeing your lock, your neighbors lock, and your two keys I cannot say with any certainty.

And a slight correction on ook, unless your keyset is an industrial lock, you don't have 10 depths. Probably 7-8, depending on the make.
posted by yoyoceramic at 8:09 AM on April 15, 2010 [7 favorites]

I know you said you acted contrary to others advice by not changing the locks when you moved in, but god for you for changing the locks now. You just don't know who the previous owners gave key copies to.

When, uh....some friends....yeah, friends, right...bought a house out of foreclosure, we, er, the friends, needed to make some repairs on the house before closing. The friends' real estate agent very helpfully forgot to put the keys back in the lockbox, enabling our friends to take the key out of the lockbox and make a copy. Bam, instant access for repairs. How often do you think something like that happens?

In foreclosure situations, there are even MORE reasons why shortcuts might be taken -- i.e, cleaning companies, real estate management companies, etc.

Whether or not this was an intentional shortcut (keying the locks on two separate properties the same, or using a lock that is susceptible to being opened by a not-quite-master-key), you should definitely change the locks.
posted by QuantumMeruit at 8:35 AM on April 15, 2010

We bought our houses within 2 months of each other from the same real estate agent.

Was the agent you and your friend used to purchase your homes also the agent that listed the foreclosed properties? If that's the case, my guess would be that the agent re-keyed the locks so that he/she would only need to carry one key to access multiple properties. If I were a real estate agent I could see myself doing something like that to keep things simple.

Just a guess.
posted by ASM at 9:05 AM on April 15, 2010

Okay, I know this is overkill, but I got curious enough about this to just brute-force the math with a perl script. (Thanks for the correction on my numbers, yoyoceramic.) A five pin key can open a lot of different doors:

5 pin lock, 7 depths, MACS=4: 10,483 possible combinations.
5 pin lock, 8 depths, MACS=4: 15,500 possible combinations.
5 pin lock, 7 depths, MACS=5: 14,407 possible combinations.
5 pin lock, 8 depths, MACS=5: 22,914 possible combinations.

Adding a sixth pin makes a big difference:
6 pin lock, 7 depths, MACS=4: 65,449 possible combinations.
6 pin lock, 8 depths, MACS=5: 168,066 possible combinations.

And for a stronger industrial lock you can get up to:
6 pin, 10 depths, MACS=5: 367,826 combinations.

(Not that any of this makes much difference if your house has windows and there are rocks available in your area, of course.)
posted by ook at 9:11 AM on April 15, 2010 [2 favorites]

Nthing that this is inevitable, but you should get your locks changed. No matter how you look at it, there is a finite number of key/lock combinations. So whether you and your friend have the same one could be a result of the agent, a developer, locks bought from the same retailer or just random coincidence.

When my dad bought a garage door opener kit for the first time when I was a kid, he made a weird habit of clicking the button anytime we were at someone's house. He thought it would be weird if someone had the same coding as his. The only one that did respond ended up being my uncle. Again, there is a finite number of possibile codes, its guarunteed to happen.
posted by whodatninja at 9:48 AM on April 15, 2010

I'm assuming when you say "works," you mean it actually opens the door, because if it just fits, that's going to happen a lot with any keys that are the same brand. [This probably wasn't helpful]
posted by ishotjr at 12:58 PM on April 15, 2010

My BIL does foreclosure inspections and cleanouts, part of that process is changing out all the doorlocks to the same key-alike code. Foreclosed homes have multiple inspectors, agents and contractors coming in and out, and it's easier for the agency to manage it this way. My guess is they never changed the locks.
posted by nulledge at 3:47 PM on April 15, 2010

These things do also happen randomly. My sister moved to a city 8 hours from where we grew up and bought a house with her then-boyfriend. His nephew came to visit and she gave him her old house keys to play with (he was 3). Weren't they all surprised when he unlocked the door with the key to our old family home.
posted by scrute at 7:46 PM on April 15, 2010

alice ayres: It's not uncommon for cars. When I worked at a hotel, the valet brought around a VW car to the front for the guest. The guest drove off but came back 5 minutes and said this was definitely not their car because things were off (mirror, seat, radio) and the license plates were from a different state. Two different guests had the same make and color and same key.

Very early one morning I got in my car at the carpark to go to work and as I sat down I couldn't work out why my seat was so far back. Or where the can of coke came from. Or where my dangly thing went.

Yeah same make and colour, someone else's car entirely. Took me WAY too long to realise.
posted by geek anachronism at 11:42 PM on April 15, 2010

And, adding to the car stories- I've also gotten into a Honda that wasn't mine, same make, model and color.

I've seen what was surely a thief with a large ring of keys, trying keys in the doors of all the cars of the same make on a street that was full of cars parked for sale.

I think that total pool of keys (perhaps for a given make/model of car) is not really all that large. I hope that the pool for house keys is larger, but I wouldn't be surprised if for a given lock manufacturer & make that the number of actual key variations isn't that large.
posted by Four Flavors at 9:48 AM on April 16, 2010

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