The Philadelphia region is great for fitness enthusiasts. But Don't let your guard down.
Personal Protection 101: Use Your Senses
If you're walking/running/hiking on the trail or in urban environments, use your senses to help detect a threat – especially at night. Yesterday, I passed three people while running on the trail. I startled them because they had earphones in their ears and didn't hear me running behind them. Take the earbuds out and stay alert. You'll also look less like an easy target.
Make it a practice to leverage all of your senses. Don't limit your ability to detect threats by, for example, listening to music with earphones in your ears while in public places – especially on dark streets at 2am.
As you're moving (or sitting), be aware of your environment by scanning in, under, over, and around structures, vehicles, trees, etc. This doesn't mean becoming or looking paranoid. Use it as a simple, natural process of observation free from tension.