Angels are astonishingly and shockingly different from humans.
You would not require "angel detectors" to spot the difference.
They appear VERY rarely.
And no angel has appeared to any human for thousands of years.
If they did - the whole world would know about it.

When they do appear to any human or humans - they tone down their appearance
as much as possible - but still have to use words like "Do not be afraid" or
"Fear not" as humans are TERRIFIED of them and their appearance.

To understand this you have to understand the relationship between angels
and God.
Which to be honest you really could not - and it would not even be worth
bothering to try to explain if some of you are so casual about angels that
you view them as a bunch of silly women who eat bananas and play cards.
THE BORG