Here’s a practical idea you should soak in: beware of people passing by and putting their hands into their pockets. Or people passing by and putting one hand behind them. You should obviously not be paranoid about them trying to stab you, but you should develop a habit of being in a higher state of alertness whenever you see something like that. It’s probably not going to be anything or it’s going to be a mobile phone, but whatever it is, you will know that you can react to it because you will have prepared. Just try to see it.