Just to the right of centre on a pre-2019 Mazda 3 is the boot release button. But move further to the right there’s a second, smaller, round button. It’s not mentioned in the owner’s manual, so what it do?

First of all, let’s clear up which button I mean…

That’s it in the centre. To put its position into context…

The rectangular button on the left is the boot release button.

So, what does it do? It locks the doors. If you’ve got out and gone to get something from the boot but haven’t remembered to lock the car (or maybe other people were still getting out at the time), rather than fumble in your pockets for your keys, once you’ve closed the boot (that bit is important otherwise it won’t work and will just beep at you harshly) you can press this button to do it.