When you're attacked what's your natural reaction? To scream, right? We all assume we can scream. But when you're paralysed with fear, no sound may come out no matter how big you open your mouth!
If you want to know what a real scream is, just drop a cockroach into your sister's or girlfriend's handbag, and patiently wait for the free demonstration.
A much better strategy is to get a personal attack alarm as shown in the pic. It fits snugly into the palm of my hand, and all I've to do is pull out the cord at the bottom, and the loud piercing sound will wake up the whole neighbourhood.
Once I accidentally activated the alarm in a hotel lobby in Indonesia. Suddenly everybody looked worried. The hotel staff even looked around the potted plants!
The alarm costs SGD $12 but if this is too much for you, get a simple whistle. I carry a whistle as well, and it always hangs conspicuously on my bagpack.
Stay safe, friends.