Once in the water, a rough wave knocked the device off his "cheap knock-off wrist-strap" and it was gone forever.
"I've got ADHD," says James. "I was much worse when I was a kid, things had to be attached to me by a string.
"I'm always thinking about lots of things at once. I'm too busy working out what badgers talk about amongst themselves to keep an eye on the myriad things I have on me.
"We have so many important things on us at once and so many calls on our attention."
He often loses items when he's tired, stressed and late or jet-lagged. In Hanoi, he left his passport in a taxi after too many rice wines, and ended up spending hours of his holiday trying to get a new one from the consulate.
James's lack of awareness also appears to have made him a target for pickpockets and thieves, who have stolen his wallet and laptop. While his poor memory is mostly confined to retaining items, he often forgets social engagements or his promises to email his mother.
These days, James goes through periods of not losing things: he'll be hyper-aware for a few weeks after one incident — and then his new carefulness will fade. "I have to do something," he said.
He's tried making up a "wallet, keys, phone" chant to recite before leaving the house, making lists and not buying so many expensive things.
"I'm organised at work," he added. "I have to think there's some hope left."
So why do some people always lose things?
More than a third of Australians have lost an item in the past 12 months, with an average value of $130. That adds up to an incredible $1.2 billion worth of valuables being lost each year, according to research commissioned by Tile, a "smart location" company that produces Bluetooth trackers.
One in 10 Aussies misplace an item each day, spending on average 29 minutes trying to find it again. On in four admit to having argued with their partner about a misplaced item, with men more likely than women to lose passports, luggage, phones and gadgets.
The most frequently lost item is a purse or wallet, and the most frequently misplaced (and then found) is the TV remote.
Seven out of 10 Australians will accept that an item has been lost or stolen if they don't find it within a week, but 15 per cent give up hope after just an hour.
Younger generations will spend longer looking before giving up, while over 65s are more than three times as likely to accept something is lost within the first hour than those aged 18-24.
AUSTRALIA'S MOST FREQUENTLY LOST ITEMS
1. Purse or wallet (34%)
2. Mobile phone (26%)
3. House keys (24%)
4. Clothing (24%)
5. Bank cards (24%)
AUSTRALIA'S MOST FREQUENTLY MISPLACED ITEMS
1. TV remote (68%)
2. Mobile phone (68%)
3. House keys (67%)
4. Purse or wallet (58%)
5. Identification document (e.g. driver's licence) (54%)