give it to a bank teller… :P

You are talking about two different denominations, if that is relevant. The bank is your best bet.

If a store gives it to you as part of your change in a store, let’s say.

Print this check lis provided by the US Secret Service, carry it on your person and check your bill against it. You need to keep genuine bills of all available denominations with you and a good magnfying glass in order to compare and contrast.

Here’s another site

“The U.S. government estimates that less than 1/100 of 1 percent (that is, 0.01%), of U.S. paper currency in circulation is counterfeit.”

Some “legitimate marks” on a dollar bill are the red and blue lines that you see if you look closely at the bill. In this link here you can see some blue lines and maybe a red one (which are harder to spot).
If you’ve ever broken a large bill at a cash register, the cashier commonly looks at it in the light. this is to check for the invisible face hidden in it. Here is an example of that. (It’s a ten dollar bill, but works for every bill).

Remember to make sure that the bill you’re looking at was printed in the same period as whatever checklist you’re working with. Currency changes over time, partly with design changes, but also because they incorporate new anti-counterfeit techniques.

@gailcalled I tried the first link it is not working, so I went Here
I was at wiki before I posted the OP.

@dxs could you let me know exact location of the red and blue lines? I think I see thinck blue line above and to the right of the second zero. I see a kind of red area above the 2 zeros. Is that what you mean?
@glacial I was thinking the same thing.

There are supposedly pens that show up differently on fakes.

Several denominations can be quickly and easily verified using ultraviolet light.

The pens that every cashier keeps are what works for them.

@filmfann the UV light thing is not that reliable. You can get round it by covering the note in sun screen. Also a genuine note washed by mistake in most modern clothes detergents will glow afterwards giving you a false positive.

Most counterfeit bills are printed on cheaper quality paper that contains starch.

Put a drop of iodine on the bill, if starch is present it will turn black/blue.

Keep in mind, a real bill could also become in contact with starch and would result in a false positive. A way to ensure that doesn’t happen is to rinse the bill with water and let it dry before the iodine test.

@Lightlyseared That simply isn’t true. Check it out.

Burn it. I think it burns with a purple flame or something I can’t really remember.

Don’t bother with the pens – they’re only accurate about 60% of the time. Most bank tellers catch fakes by how the bill feels. If you touch enough real bills, spotting a fake that way becomes easier.

The first things I look for are the red & blue fibers, the security strip in later bills, microprinting and crispness to the portrait.

@flo the red and blue lines are scattered throughout the bill. Once you notice one then you can easily find the others. You just have to adjust your focus.

Thanks all.

I see some people who just go by feel, I guess they’re most likely cachiers. That is really what I meant by “the fastest way”. To correct myself, there is no longer a bill larger that $100 so there wouldn’t be part of change.

BTW, can you get a counterfeit bill from the ATM? I heard a while ago that that can happen. Shouldn’t the bank be the one place you would count on not to have this problem?

If it’s a very very well done counterfeit, a less experienced teller might not catch it. If that teller is the one who happened to count the strap of bills that contained the counterfeit and loaded them into the ATM, it’s very possible that it got missed. While there are cash counting machines that can detect counterfeit, not all banks have them.

@tedibear Okay.
Are the banks required by law to have them?

No, they’re not. A regular cash counter costs between $250 and $350. A counterfeit detecting cash counter can cost from $600 on up.

The U.S Treasury estimated that in 2001 less than .01% of the approximately $600 billion dollars in circulation is counterfeit. Unless that specific bank (or branch of a bank) tends to find counterfeit on a regular basis, they’re unlikely to invest in that machine.

Interesting.