When we think about improving something we often think of making it easier to use.

Sometimes the opposite is true. Like this alarm trigger on a Perth train.

The trigger has to be immediately obvious and accessible. But the barrier to triggering must be high so as to avoid unintended activation.

Good design in this case addresses two different contexts. In the everyday context, this switch much be visible but hard to accidentally trigger. The position, brightly coloured recessed button and plastic cover flap work together to achieve this.

In the context of an emergency, the switch must be visible, accessible and obvious to use. Lift flap to access the button, and press it to activate; with presumably some instantaneous feedback.

The user interface of operating systems use a similar design principle for actions that must be easy to trigger but not too easy. Especially actions that have significant consequences and/or are not easily reversible.

When we attempt to delete a file, we often need to confirm our intention before the deletion will occur. This is the software equivalent of the plastic flap and recessed button we will first see a dialogue box. Much like the plastic flap.