Travelers "tipped" the TSA nearly $1 million in forgotten coins and currency in those plastic bowls and bins while struggling through security checkpoints at airports last year.
The Transportation Security Administration said passengers left behind $867,812.39 at airports around the country in 2016, reported CNBC.
That total marked a continuing trend for left-behind change, the TSA told CNBC. In 2011, passengers left $489,000 at checkpoints. In 2014, they left $675,000, and $766,000 in 2015.
Congress passed a law in 2005 allowing the TSA to keep unclaimed cash left at checkpoints and spend it on aviation security efforts at its discretion.
Airport checkpoints can prove to be an arduous task for most passengers, where they are asked to remove all metals – including coins – from their pockets, take off their shoes, and remove laptops from their carryon bags before going through a metal detector.
They are asked to do this knowing that throngs of other people are watching them complete the task so they can do the same while on the way to their airport gate.
"There is no real way for TSA to know why this happens," said TSA spokeswoman Lisa Farbstein. "It makes sense to point to an increase in the number of travelers as one likely reason, but other than that, we have no theories."
The U.S. Department of Transportation's Bureau of Transportation Statistics reported in March that U.S. airlines transported an all-time record 823 million passengers in 2016, 719 million domestic and 103.9 million international. The old record, 798.2 million, was set just a year earlier.
Despite the increasing loss of loose change, Michael Taylor, director of airport practice at J.D. Power said in January that customer satisfaction at airports is improving, according to the website Business Traveller.
"Many airports, especially the nation's largest airports, were never built to handle the current volume of traveler traffic, often exceeding their design limits by many millions of travelers," Taylor said.
"Yet airports are overcoming infrastructure limits by affecting the things they can influence. Airports are successfully applying technology to improve check-in (up five points in traveler satisfaction in 2016), security screening (up 3 points) and the food, beverage and retail shopping (up 10 points) experiences."
CNBC said TSA has used the left-behind funds to improve and expand its pre-check program that gives passengers faster screening privileges. Some airports gave leftover cash to charity.
In 2016, Denver International Airport donated $87,106.91 to Denver's Road Home, a non-profit that works with service providers for the region's homeless community while the Phoenix Sky Harbor International gave more than $11,000 to help support the USO operations at the airport.