> require written authorization by the landlord

How are they going to even know?

> ...you can't waltz into...

I've never come across a key that couldn't be duplicated with a quick £5 waltz. IME only I suppose.

For example : [1] & [2]

Only the entity ordring the locks is authorized to have additional keys made. And it's pretty heavily enforced by the manufacturers and distibuters.

Copies are also more than 5 quid.

[1] https://www.dormakaba.com/hr-hr/proizvodi/proizvodi/mechanic...

[2] https://www.assaabloy.ch/en/local/switzerland/landingpage/as...

Edited to add : While the web pages talk pretty much about smart locks, both manufacturers offer purely mechanical locks (or hybrids), which cannot be copied easily.

Maybe it's that I've never rented a nice enough place, but all my past landlords have chosen the £10-a-lock non-patent-protected locks over the £100-a-lock high security locks.

My landlord in the US uses cheap locks, he said he throws them away after each lease and puts in new ones. It was lucky for me one day when I forgot my keys, but had my lockpicking kit in my backpack. It took about 5 minutes to rake both the knob and deadbolt and get in.

where i live, it's customary to either re-key your door after you rent a new place or just exchange the whole lock.

as long as you give back two copies of the key by the end of the lease, landlords usually don't care.

Those are very high end ones I'd expect to see on commercial installations or homes of the ultra rich. Most landlords in my part of the US use the cheap regular off-the-shelf locks, where you can copy the key for a couple of dollars at Home Depot and throw the lock out once the tenant departs.

>How are they going to even know?

Because it's a non-standard key with print on it: "Property of X, not to be copied without permission" and because it's a non-standard key, to even get the blanks requires knowing whom to ask for permission to make copies.

Think something like US Post Office box keys, or bank safe deposit keys.

"Property of X, not to be copied without permission"

Not even that. The keys I was referring to have serial numbers and the blanks are strictly controlled.

Only the owner of said serial numbers (usually represented by a card) can order copies directly from the manufacturer or their designated agents.

Normal key copy shops wouldn't even have the blanks to furnish copies.

I don't think that it's totally impossible to copy such keys and it will be probably even be harder to prevent copys in the future (think 3d printing). But you can't have them copied by any old shoe maker with a key copy side business.

Back in my university days they would only give us one key to a room that was designated for our club. They had the special blanks with the second set of teeth on the inside.

I just found "normal" blanks with the same cross section, whipped up the tooth profile and a holding fixture in some pirated CAD program and took a thumb drive and the blanks down to the machine shop during lab hours.

Anyone who knows how to use a machine shop can duplicate any key. For most keys there are specific machines that don't require skill to operate that duplicate it. The skill required to duplicate the other keys, combined with the "do not duplicate" stamp on the other keys means that such keys are rarely duplicated.

In the vast majority of the US, there is no law against businesses duplicating keys stamped with "do not duplicate" which means it's usually not too hard to find a shop that will do so.

That depends. You are legally correct. Most shops when seeing a do not duplicate key will do some checking to see if you should be allowed to duplicate the key (but there is no standard here), compared to any other key which they will duplicate no questions asked.

Also some "secure" keys don't have any blanks. Most shops don't have the ability to duplicate them. You can still get them copied, but you need a skilled machinist at considerably more cost.

> I don't think that it's totally impossible to copy such keys and it will be probably even be harder to prevent copys in the future (think 3d printing). But you can't have them copied by any old shoe maker with a key copy side business.

I remember a story recently about a secure luggage key. And every luggage lock was supposed to use it, but you weren't supposed to be able to get copies. But then a newspaper article printed a full-page image of the key, so... yeah, it got duplicated on a 3D printer that day: https://nakedsecurity.sophos.com/2015/09/11/tsa-master-lugga...