Startup Idea : SOS app based on decibel meter for distress

There are already apps which are designed for sending an sos message or a distress sms. Situations like accidents,rape,murder etc happen suddenly where victim does not have enough time to press a panic button or sos on a smart phone.There can be a simple app which measures the decibel level.If the level crosses a thresh hold then immediately an sms is send.A person always screams in distress.This voice is measured and a sos message is automatically send.There could be scope for further tuning of this app to reduce false positive.