From pocket to carry-on immediately before security in Newark, back to the pocket after that scan. Same in Atlanta if you have to go through a security scan there for whatever reason. Immigration and customs would be done in Mexico and I would just keep it in my pocket there.

Another question you might ask would be if there was any customs duty for importing that ring. I would suppose not.

I assume immigration and customs in Mexico don't require you to empty your pockets too?

You don't go through customs on an outbound flight. Customs deals with the importation of goods into the US. Connecting in Atlanta, you probably will not even go through security if you're flying Delta as it appears Cancun flights leave from the domestic gates.

As others have said, I doubt there will be a problem arriving in Mexico. When returning to the US, your fiancée will presumably be wearing it, so it shouldn't raise any questions there either.

It probably wouldn't be a bad idea to take a copy of the receipt with you. If you do have to prove the value of the ring to border agents, or if (heaven forbid) it goes missing and you need to file a police report, you'll have something to prove you had it and what it was worth. With a copy of the receipt, you'll still have the original safe at home.

Lastly, you may want to stash it in the hotel safe until the appropriate time to prevent it falling out of your pocket or your girlfriend accidently coming across it in your luggage while looking for something.

Maybe I'm just a Nervous Nellie but with the changes in flights, TSA, scanners, etc I would bring a fake ring to propose with and leave the real one at home.

Thanks for the advice. I do plan on bringing a copy of the receipt for proof of purchase. Correct me if I'm wrong, but isn't customs arriving in Cancun where you get your passport stamped and bags scanned? I've flew into Cancun a long time ago but didn't have an agenda like I do now. I don't really recall the process. It was also a direct flight from Newark, not a layover.

Customs is interested in goods you might be importing to the country (contraband or merchandise for resale), so they will not be interested in you. You will go through passport control, though.

Okay, let make this clear.

In EWR, you go through security. Everything carried-on will have to go through X-ray scanner. You can put the ring in any of your bags or shoes. The danger is there's a rogue TSA agent who notice the ring from the scan and then steal it. So, keep your sight on that item for as long as possible and check it soon after.

After you get to Cancun, you'll go through Mexican immigration where your passport get stamped and then customs. I haven't flown into CUN, but if it's like 99% of the airports around the world, you only have to empty your stuff if you declare to be bringing more than the allowance, or if you are stopped for random screening. I don't believe Mexico has value limits you bring into the country for your own use and is bringing them out (i.e. you're not gifting it to a local in Mexico).

On your way back, you will go through security at CUN, where your fiance won't be asked to take the ring off. And then you through US immigration and customs after you arrive, where again, it won't be an issue unless they suspect you're brining more than US$800 worth of goods obtained abroad and not declaring it - this is where the receipt may be helpful, but everyday people wear jewelry worthing thousands and tens of thousands in and out of airports in the US with no problem.

Yes you go thru both Immigration + Customs when arriving Mexico. They do not care about a ring.

I worry more about it potentially setting off a metal detector at TSA when initially boarding at your home airport and ruining the surprise.

Metal detectors do not usually ping for small items of gold. At least I've never removed rings, gold chain with dime-sized pendant, or earrings for TSA.

I believe customs is concerned with illegal items (drugs), prohibited items (fruits, vegetables, plants), cash in excess of $10,000, and items you intend to sell. As rkkwan pointed out, people travel wearing jewelry everyday, and we're assuming your GF will be wearing it on the journey home.

The ring won't set off a metal detector, but the OP will be asked to empty all items from his pockets if they notice a bulging ring box. Of course he can NOT use the box, but if he gets the full body scanner - not sure if those are still used or not at EWR - they he'll be scolded (if not worse) for not removing all items from his body when they see the ring in the scan.

Carrying receipts for expensive jewelry, cameras, and such is always a good idea. It used to be possible to register the items with Customs at the departure airport so there was no chance of duty's needing to be paid on return to the U.S.

Can you possibly wear the ring on your pinkie? If it won't fit, then put it in a chain and ear it around your neck prior to going through TSA. AfFTER clearing, take it off pinkie or chain and put it back in box, in a very safe place. I would not put it in a pants pocket, but rather in a zipped pocket or shirt pocket. Congrats!

Agree with debit...take it out of box and wear through the scanner...just turn it around so diamond is underneath. That will be safest for you...

And how can you make the GF not notice it?