What am I?

I can be in your room and your mind but two people can never find me, What am I?

related riddles

I am a protector. I sit on a bridge. One person can see right through me. Others wonder what I hide. What am I?

I am black when you buy me, red when you use me, when I turn white. You know it’s time to throw me away. What am I?

Forward I am heavy, backwards I am not. What am I?