"Chilla" is a personal safety & security app that can be triggered by just a shrill scream . It totally removes the hassles of unlocking the phone or opening the app. It has been found that in cases where someone follows a girl / women or eve-teases her , she generally doesn't calls out to parents or police and if they attack her , the app is of no use to her then. In that situation scream is a natural reaction and tapping that is the best possible way to bring her help.