Thanks for all the replies!

My student Union runs self-defence courses that I have attended. They're aimed at teaching awareness of risky situations, increasing your confidence and teaching simple defensive moves.

As i live in the UK, being armed with any sort of weapon is (as far as I'm aware) illegal, and therefore not an option.

I think its the same for pepper sprays and electronic stun devices.

These attack alarms are not designed to attract help because as pointed out by other posters most people don't want to get involved.