Work through these in order.

If steps one to three solve it, nobody needs to come. If they don't, steps four to six decide how long the visit takes and whether the lock survives it.

A locksmith on the phone is trying to picture the door. The more of that picture you supply, the better the chance that the blanks and spare cylinders in the van match what is fitted.

For each external door on each managed property, record:

- Lock type: Deadlatch, deadbolt, mortice lock, rim latch, multipoint lock, sliding door hook lock or digital lock. A single door can carry two of these (a deadlatch and a separate deadbolt, for example), so record both.

- Make and model: Look for a brand name on the cylinder face, the keyhead or the inside cover. Write down what you can read; a partial name is still useful.

- Cylinder profile: Round or Euro-profile. If it is a Euro cylinder, note its size as well.

- Keyed alike or not: Whether the front, back and side doors take the same key.

- A clear photo of each lock: Taken from the outside with the keyhole visible, plus one of the inside handle or turn.

Some cylinders carry a code stamped on the body that corresponds to the key cut. Record it, but keep that part of the file locked away, since that code belongs with the key records, not on an open file.

Hardware varies with the age of the door: an original mortice lock or rim latch calls for a different approach from a multipoint lock driven by a gearbox in the door edge, and the locksmith wants to know which one is waiting before arriving.

If a property sits on a master key system, a keyed-alike set or a restricted key profile, the record needs the details that tie each door to that system.

A spare key in the right hands ends a lockout without a call-out. A spare key nobody can find, or one that nobody is cleared to hand over, adds a step and a delay.

Record, for every property:

- Where the agency spare is held: The office key cabinet, a safe or a lockbox at another site. Record the hook or slot number, and keep the street address off the tag.

- Who can sign it out: Name the people at the agency who may release a key, and what they need to see first (photo identification showing the address, for example).

- Whether the owner holds a set: Some owners keep their own keys. Note whether they do and how to reach them.

- Whether the spare was tested: A spare cut years ago may no longer match a lock that has since been rekeyed. Check it against the lock at each changeover.

A locksmith opening a door for someone who is not the owner will ask for proof that the person asking has the owner's authorisation, and for identification from the person being let in. Photo identification showing the address is the starting point. For a managed rental, the locksmith may also want to see that the agency can arrange lock work at that address.

What helps here is a short, signed note from the owner, kept in the property file. It names the agency, the address, and the staff who can approve locksmith attendance, lock repairs, rekeying and lock replacement on the owner's behalf. It also says whether there is a ceiling on what can be approved without a further call to the owner. Send a copy to the locksmith when you book the job, or have it ready to read out.

That note answers a narrow question: who can engage a locksmith and approve lock work. Whether a particular person may be let into a particular home is a separate matter that depends on the tenancy and the circumstances. Rules vary by situation, so check the current rules for your property and your agency's process before a lockout tests them.

The changeover is the one moment when the property is empty, the keys are back in your hands, and you can see every lock. Use it to bring the record up to date.

A lockout is never convenient, but its shape is set long before the phone rings. The managers who get through them quickly are the ones who treated the last changeover as a chance to write the lock down properly, kept that record secure, and could read it out without hunting.