|Euro profile lock
It is actually surprisingly easy to change the locks. They are held in with one screw, but obviously you have to have the door open to remove the screw, and you have to have the key in order to turn the lock slightly to align it to remove from the door. You may have to remove the door handles as well.
I only changed the lock as we managed to get a key break off in the old lock, but I also noticed my locks were old which means they are vulnerable to a number of types of attack - not just lock picking, which is not that hard on older locks, but also tricks to break the lock at the weak point and remove it.
Then you need to turn the lock (though one of our locks was very old and could be removed without doing so). When you have it right (slightly anti-clockwise from the external side) you can push or pull the lock out of the door.
Fitting the lock is the same in reverse. I did find I had to remove the handles to get the lock to slide in and out more easily.
To buy a new lock you do need to know the size. There are lots of sizes. You need to measure the old lock, in mm. This lock is 90mm, and is 55m external and 35mm internal, which is measure to centre of the part that turns in the middle. You should get the internal and external the right way around. You may find you can have 5mm more than you need as that just means the lock sticks out (as show top right). You should try and avoid the external side sticking out if possible to make it harder to attack. (Thanks to Mat for pointing this out). There are different types of lock - you can have keys both sides or a thumb turn (as shown here).
|90mm long, 55mm external, 35mm internal.
|Old and new keys
There are different levels of security. I went for a Yale Superior Series. It does not have cuts in from the edge, creating the weak points that allow keys to so easily bend or break, but parts milled in to it. These seem to be two different angles on one part and a groove (so a 3rd axis) on the other part. Clearly this makes it a hell of a lot harder to pick such locks.
The company I bought from (Lock & Key) were very good. They can cut new keys as needed (using the 13 digits of code provided).
What is quite nice is that they can make all the locks the same key if you want. When we moved in and then had double glazing fitted, and then a conservatory, the end result was five separate locks on this house. Now we have just one key for all it is much simpler. Now we have somewhat better locks, we should be more secure. The objective is that we are harder to break in to than next door, so better locks is one step in the right direction (as is security cameras and the alarm system).
|Three different axis of coding
To be fair, the same is true for the old style keys, but even simpler. The only real way to avoid this is with electronic keys, and even then you need active keys with challenge./response coding. That is possible in higher security locks. But as I say, you just need to be more secure than your neighbours.