It is the first question almost everybody asks, and the honest answer is: usually yes, sometimes no, and you should be told which before anything starts.
What “non-destructive” means
It means the lock is manipulated into doing what your key would have done. Nothing is drilled, cut or levered, and when the door opens you keep the cylinder and the keys you already own.
The techniques differ by lock type, but they all rely on the same idea: a mechanism built to be operated can generally be operated by something other than its key, given knowledge and time.
Time is the part people underestimate. Non-destructive opening is skilled work, not a magic trick, and on an awkward lock it can take longer than drilling would. A locksmith who chooses the slower route is usually the one saving you money, because the fast route ends with a bill for parts.
When a lock cannot be saved
Four situations where damage becomes likely or certain:
The lock has already failed. If a spring has gone, a cam has sheared or the mechanism has jammed internally, there is nothing left to manipulate. The cylinder comes out and a new one goes in.
A broken key is in the cylinder. Sometimes the blade can be extracted and the lock saved. Sometimes, particularly after someone has attacked it with pliers, it cannot.
The door has been forced. After a break-in, the frame and the lock case are often distorted. Getting in is the easy part; the repair is the job.
The cylinder is built to resist exactly this. High-security cylinders are designed so that manipulation is impractical. That is what you paid for, and the price of it is a drilled cylinder on the day you lock yourself out.
Drilling is not vandalism
There is a difference between a controlled drilling and damage. Done properly, a cylinder is drilled at a specific point, it fails, the door opens and a new cylinder goes into the same hole in the same door. The door leaf, the handle and the frame are untouched, and the cost is the replacement cylinder.
Damage is a drilled handle plate, a chewed door edge or a frame levered apart because it was quicker. There is no reason for any of that on a routine opening.
Questions worth asking on the phone
- Will you try to open this without damaging the lock first?
- If it has to be drilled, what does the replacement cylinder cost, fitted?
- Is that total the price I pay, including the call-out and the hour?
- Will I keep the old lock?
Four questions, thirty seconds, and they tell you a great deal about who you are speaking to. Anyone unwilling to answer the second one before arriving is someone to be careful with.
What you should see on the day
You should be standing there. Nothing needs to happen out of your sight, and the method being used should be explained in a sentence before it starts.
If the cylinder has to go, you should be told before the drill comes out, not after. And when the old lock is removed, ask to see what was wrong with it. A locksmith who cannot show you why it failed may not have had a reason for replacing it.
If the door itself is uPVC or aluminium and will not open even with the right key, the fault is usually the mechanism rather than the cylinder: that is a different repair, and a different conversation.