I've been looking for one of these for a while, but at £19.50 it was way too expensive. This device has very good reviews on the M&S site and at various other sites - just search in Google.
But now they're half price at M&S - £9.75. I managed to use a code for 10% off women's wear and got it for £7.80, delivered to store. The code I used was: PERWEBI5
A unique and revolutionary personal safety alarm for women. If you're attacked the adrenalin in your body can cause you to lose your voice. This small alarm emits an extremely loud female scream designed to shock and disorientate your attacker, giving you a chance to flee.
This stylish alarm is designed as a discreet accessory that can be kept close at hand - attached to a key ring or clipped to your handbag. To activate, simply pull sharply on the chain.