How does Security detect liquids in carry-on bags?

Question

TSA always tells you to take your "3 ounces or less of liquids/gels and put them in a clear, 1-quart plastic bag and sed it separately through security (carry-on bag security) from your backpack". My question is, IF you DON'T put the liquids in the 1-quart bag, and send it through the scanner separately, and say, just leave in amongst the other stuff in your backpack, HOW DO THEY DETECT YOU HAVE A LIQUID IN YOUR BACKPACK? Does the scanner w/ the X-ray detect it? Or will they have no idea? I'm saying, like leaving a 2-ounce jar of water in your backpack under other stuff? What will they do if they find it?

Answer 1

They often look through the bags by hand. I suppose occasionally something could be missed. And "common lighters" are allowed.  See site below to verify that.

Answer 2

I honestly don't know how he got a lighter on board, it seems like something you shouldn't plus it's illegal to smoke on a plane, so he wouldn't need it except from the airport, but i just know they do detect it.

Answer 3

i believe ion  analyzers are what your after as in particle analysis

Answer 4

If anything looks like a container, they search by hand.