I've noticed on posts about EDC and Urban survival kits that one thing people don't seem to carry is personal attack alarms. I guess this is more directed at the women of the forum, but also the men.

My Students Union and the local police force advocate (and provide free of charge) personal attack alarms. These are devices that can be carried that when triggered produce a very loud (in excess of 100decibals) siren that is designed to briefly shock your attacker and allow you precious seconds to run away.

they are either battery powered or run on pressurised air. Once activated by either a button or pin they sound continuously even if dropped.

While if I was mugged, I would immediately give up my bag in preference to being attacked, these devices are useful to have accessable on your person if you are out alone..

Is there a reason why people don't carry them?