Im not a professional at all but I do practice most of the things mentioned here and I just wanted to add to this excellent post;
Predators often seek out people who seem unawares, distracted, injured, head down, texting. Get in the habit of scanning 360 degrees and being hyper aware of whats going on around you.
Even if youre just walking down the street. Ive had people come off another street and walk in step behind me right in my blind spot. When that happens, I calmly turn around and make eye contact with them. To let them know that I know they are there and to give them the hint they need to back off a bit. Most do, and I'd be very concerned about someone who didnt.
Keeping our eyes open seems simple but I fuss at my wife and son all of the time about not having any spatial awareness.
Agreed, awareness is key - and especially in "transitional" areas, by which I mean going from a presumed safe place to one that's not - people often get in a "bubble" of complaceny in and around such places. Think of areas around airports and transit stations, mall, shopping center, and bar/restaurant parking lots, and apartment parking areas.
You have to consider the threat - thieves and robbers like to target airports, and nearby hotels and restaurants, because business travelers often carry expensive electronics - I live near an airport, and rental cars were targeted by a theft ring in local restaurant parking lots, due to the correct assumption that many business people left laptops in their cars.
After a colleague was robbed outside an airport, I made a special point to raise my awareness in and around them. And in doing so, I came to realize that certain airports are full of would-be predators- I could tell, just by watching people outside the security areas, and seeing certain of them being entirely too interested in passers-by. I've silently intervened more than once when I've noticed someone get up suddenly to follow someone, veering close-by to the person being stalked and locking eyes with their pursuer. I've been given hateful looks, but more than once, the pursuer just gave me a rueful smile, or shrugged, before turning away. In the US, Northern CA airports, like SFO and SJC are particularly bad - you'd think "Oakland", too - but it's not as bad as the others - fewer presumed-wealthy tourists and business travellers transit there.
With awareness comes something else - your instincts. Evolution gave them to us for a reason - learn to listen for them, and what they're telling you.
As for self-protection devices, don't carry them (only) in your purse. In your pocket, in your driver's side door bin or clipped under your visor , velcro'd to the inside trunk lid.
It's not Mogadishu out there, no need to live in fear. But don't let embarrassment prevent you from taking modest safety precautions.