In addition, some cars - I don't know if this is legislated or a feature - will blink the brake lights or even the alarm lights if it detects a sudden hard brak

In addition, some cars - I don't know if this is legislated or a feature - will blink the brake lights or even the alarm lights if it detects a sudden hard brake (emergency brake). But people would do that themselves anyway if they for example had to slow down suddenly due to a traffic jam or whatever.