There are lots of personal attack alarms on the market but this is generally accepted as the best and certainly the loudest.

Activated by removing the pull cord it sounds immediately.

The sound is painful close up and the light will help people locate you in the dark. Small enough to fit discreetly in a pocket or handbag, with attachments to fit on a belt, bag strap.

Keep one in your car, behind the front door and on your person.

Also recommended for people liable to suffer from an emergency medical complication.