Someone cryptographically attacked my bike!

Now we're playing cat and mouse.

I’ve been playing cat and mouse with a stranger. And I’m risking €1200 and have nothing to gain.

I rented a bike to get around Berlin more easily. It has a combination lock.

Usually, I’m quite lazy, so I only change one digit. After all, who would know I only changed my last digit. I park it in a tucked away alley, so no one can observe me doing it. You could probably guess that I’m not properly randomising the code just by the time it takes me to unlock it. But there is no one to see, so I’m safe. Or so I thought.

But there is another way of finding out that I only change one digit. Just look at the code between my rides, e.g. at night, when the bike is parked. Say, you observe the following:

Night 1: 2-1-1-1
Night 2: 7-1-1-1
Night 3: 3-1-1-1

You can safely assume that I’m just changing the first digit. Therefore, the code is
X-1-1-1.

What about if I change a random digit (not always the same one):

Night 1: 1-8-1-1
Night 2: 1-1-3-1
Night 3: 2-1-1-1

The malicious observer clearly sees that I’ve been using the bike in the meantime, because it’s parked at different spots. But it doesn’t take a genius to figure out that only digit is being changed and it’s safe to guess that the code is 1-1-1-1.

How do I know someone was trying this. Well, I only changed one digit found the lock in the following state: 3-3-1-1 although I left it with 3-1-1-1.

So now I always change my code to the same combination (but I only still only change one digit to safe time), so it looks like this:

Day 1: 7-1-1-1
Day 2: 7-1-1-1
Day 3: 7-1-1-1
Day 4: 7-1-1-1

I also changed the combination to a relatively similar one, just to frustrate the thief.

What do you think? How much less safe is it use my strategy instead of randomising completely every time?