How do you sense that you are in the presence of a vampire?
Many vampire stories tell of special powers that come to the forefront once a human is turned to a vampire, making it seem that vampires have extra sensory powers that humans do not. In fact, humans have deeper sensory powers than vampires do, we just have been conditioned over time not to connect with them.
One of those strong human senses is the ability to detect evil. We grow up told we have five senses: taste, touch, sight, hearing, and smell. Well, these are indeed all of our most heightened senses, but they are not in any way our only ones. Our ancient ancestors have named over 300 different human senses, and believed that there were likely more that we were not yet able to use.
These extra-senses are often lumped into one condition we simply call "the sixth sense" or "extra-sensory-perception". In truth, there is nothing "extra" about them, nor is it just one extra sense, but hundreds of them. Identifying them in this lifetime is no easy task, especially when we have been conditioned to believe that they don't exist. They don't ever "die out" though, and you can train yourself through practice and meditation to heighten these senses if you needed or wanted to.
We've all been in situations where we instinctively felt fear. This is a survival instinct that lives at the core of us all. Similarly, when we are around evil, we can feel it. Regardless of what teenage fiction novels suggest, there is little reason to believe that one might run into a vampire and become best friends with it. These are those who have given up their souls for power, and if you've ever met someone in this world who has figuratively done the same, it's doubtful that they would have your best interests at heart.
In all respects, vampires, demons, and other dark spirits are all dangerous to humans and should be treated as such. These beings intentionally use charm and lies to trick humans into overriding their inner senses and trusting them. If you encounter one of these beings, or are unsure about someone, always trust your senses. You do indeed have a way of detecting the presence of darkness. I can't explain to you what it is or how it feels, but you'll know it when it's there.