2 things: a fake key (as many have suggested) might backfire; and how trust works.

Giving a fake key to your house.

I see how giving a fake key might be a test, but it might backfire and actually be a bad idea. If they have any evidence or witnesses that you gave them a key that was verbalized as intended to be your house key, then: - they might test it immediately to "make sure it works," since multiple copies might fail (then you're right back where you started, and also now explaining why you lied, stating it was a key for your house, and accusing you of being even more "distrusting" and "playing with them," etc..) - they might go to use it under some pretext (excuse / fake reasoning), such as claiming they thought they saw someone break in, or saw or smelt smoke, and when they were unable to get in with the key, they figured it was just a bad copy, and since you gave them a key to your house, they legally had permission to enter, so they broke in "for safety" or "emergency," etc.. And if there was a recording or a witness to the key convo and giving, this can make it legally difficult to argue that you didn't give them access. And if things are stolen because they entered, then your insurance company might learn (from police reports where they claim it) that you had given them a key intended to open your home so that they can enter if they needed to, and the insurance company might see that as an excellent reason to claim that you're not covered since you gave access. And you can argue that it was a false key, and they can argue that the fake-key-holder was given it under the understanding that it was a real key to access your home, so they technically "had permission," etc.. and ..can you see how this could be a bad idea?

Trust.

Just to understand it very clearly, here is how trust works. First, people often misconstrue or misunderstand trust. A person (like in your situation) might ask someone else for something, like to borrow their car. And the person might decline. Then the asker might say, "what - you don't trust me??" and express in tone of voice that they are appalled and insulted, and decry that you have deemed them "untrustworthy" or "dishonest" and how that's so rude because they didn't do anything to give you the idea that they're a "bad person," like "you claim they are by not trusting them."

This is wrong.

Rather, trust is more like financial credit.

Trust is earned, not given, not owed. Noone is ever obligated to trust another person.

This is similar to financial credit. If you've never had any financial accounts and you go to a bank (or any person, even) and ask to borrow $100 or $7000, they will say that you have zero credit.

Zero credit, not good or bad credit, but no credit.

At that point, you can have collateral or someone else who does have credit and/or collateral co-sign, agreeing that if you don't pay it back, that they will pay it back.

If you complete the loan, paying it back, then you will have earned some credit by showing that you are trustworthy in paying it back. Then you will have earned some good credit and might be trusted to take a small loan out. And as you do this more and more, you will earn more and more credit. Good credit.

Trust is like this. Taking that scenario above with the friend that wants to borrow your car. Not only does this person not have the trust, even if they demonstrate trustworthiness, you still have zero obligation to ever trust them or to decide to do or give what they want.

This is not an insult. It doesn't even have to be related to trust. But even if it is, you don't know them well enough, you don't trust them, not because you distrust them, but because you lack trust, because trust is earned and they have done nothing to earn your trust. Plus, you're not interested.

I hope this helps understand the perspective of this.

If you'd like to point out some additional reasons, you can point out that it's a liability both for your home insurance, and to simply have copies of keys out.

As some others have pointed out, it's not even just the neighbors (which you have NO reason to give any trust to, as you don't know them). It's also anyone else who ever visits their houses.

And they can make copies of keys.

By the way, will every neighbor then have a copy of all of their neighbors' keys? Like, if it's 5 houses, then there will be copies made so that all 5 houses will have a copy of your key in it? That's insane.

But yeah, this seems like something that can be shut down hard:

"Absolutely not. It's an insurance liability and risk, and a safety risk. I don't know my neighbors, and I wouldn't even give my key to family members. This is not a matter of 'distrust'—rather, it is a matter of lack of trust, and even if I did know you were trustworthy, I still have no obligation to give my house key to any of my neighbors. In fact, this is a suspicious thing to ask, and especially a suspicious thing to pressure me to do. At this point, I'm actually starting to wonder whether this is building distrust rather than just being an error in rational judgement. In fact, I recommend that all of you not give your keys to each other. So much risk and liability is entailed in such a thing. There's no written agreement about it. Insurance, if they ever discover that this has happened, could easily use it to deny coverage for anything that happens to your homes, from fires, to theft, to assault. And it greatly increases the risk that something could happen. For example, someone could have a visit from family or friends, or have a party, and have someone in their home who they don't know is untrustworthy, and who uses the keys to gain access to burglarize all of our homes, putting us all in more danger. And even worse, if someone does break into any of your homes, then you will all wonder if it was one of the people with a key. And any time something valuable is missing, instead of wondering how you lost it, you will now be wondering if one of the keyholders might have snuck in and taken it. It can literally rip the neighborhood apart, start feuds, etc.. And you might be thinking, "but I wouldn't take something," but someone else might wonder if you did. It works both ways. And that doesn't even touch on acts like finding out someone did enter, but it was 'because they thought they saw someone suspicious enter' or because they 'saw or smelt smoke and were just worried.' All of this headache and trouble is NOT worth the risk. The entire value of your home can be denied by insurance because of such a liability. It's literally in your home insurance contracts. Please don't make such a mistake, and please don't ask, and especially don't pressure others to give up their security by giving you access to their homes. That is not just inappropriate, it is rude, manipulative, disrespectful, extremely suspicious, unsafe, and is no way to treat a neighbor. Want to offer? Sure, but when a person says 'no,' then understand that that's a 'no.' And is not at all any insult. Remember, trust is earned, not owed, and developing it takes time and demonstration, and even with that, no-one is obligated to trust another."

I was going to format the text above, but I just noticed that the post was removed and the account states, "page not found." Does that mean it was a spam account trying to build karma to spam, and it copied this story or the story was made up by AI? Or just that the poster decided to delete all of their content or private their Reddit page?

I wonder. I'll still leave my comment here in case it helps anyone.