Answer:
In a tunnel of darkness lies a beast or iron. It can only attack when pulled back. What is it?
Never ahead, ever behind, yet flying swiftly past, for a child, I last forever, for adults, I'm gone too fast.
Some try to hide some try to cheat. But time will show we always will meet. Try as you might to guess my name. I promise you'll know when you I do claim.
I am a mini solar powered computer
I am a protector. I sit on a bridge. One person can see right through me, while others wonder what I hide. What am I?