The hundreds of thousands of Americans who bought a drone in 2015 face a key deadline Thursday. It's the last day they can comply with a Federal Aviation Administration mandate that they register their device without paying a $5 fee.
But one day ahead of the deadline, it appears that a sizable percentage of drones will not be registered. What's more, experts say it's not at all clear that even a successful effort will achieve the agency's goal of preventing a disaster from the reckless use of one of these devices.
The FAA requires consumers to register unmanned aerial systems, or UAS, that weigh between 0.55 and 55 pounds. The rules aim to keep track of the booming technology and prevent potentially dangerous flights around planes, airports and public events.
Earlier this month, FAA Administrator Michael Huerta said the agency was "encouraged" by registrations, which topped at least 180,000 as of Jan. 6. Users registered for free for the first month, but pay a $5 fee if they sign up after midnight Thursday.
While the charge is modest, it adds a potential hurdle to the already difficult process of getting users to register and understand how to properly use a drone.
"I have significant reservations about the effectiveness of the registration process, though something is better than nothing," said Troy Rule, an associate professor of law at Arizona State University who studies airspace regulation.
The Consumer Technology Association estimated 700,000 drones would ship last year, a 63 percent increase from 2014. The registration process came in response to that increase and hundreds of "close calls" between drones and commercial aircraft.
Related: Drones Fly Through Obstacle Course Without a Ding in Researchers' Video
Drone owners who fail to sign up could face criminal and civil penalties.
"Simply put, registration is all about safety," Huerta said this month at the Consumer Electronics Show in Las Vegas. "It provides us with a key opportunity to educate the new generation of airspace users that as soon as they start flying outside, they're pilots."
More from CNBC: Consumer drone registry creates challenge for FAA
But Rule said the registration program, while a step in the right direction, may not give pilots enough flight training.
When users sign up, they receive some guidelines, such as keeping aircraft within their line of sight or not flying over crowds. Leading drone producers such as DJI and Parrot have also included safe flying instructions in their packaging.
Still, the FAA does not require UAS owners to take a test to prove their knowledge, whether written or practical like driver's license exams.
"The FAA has done a good job of making its stuff pretty user friendly. But it's hard to say how effective that's going to be, given there's no test of any kind," Rule said.
Related: Passenger-Carrying EHang 184 Drone Unveiled At CES
While the FAA believes the registration rate has been strong so far, hundreds of thousands of drones remain unregistered. The fee that takes effect Thursday may not help.
Rule contended that the $5 charge may only have a "small effect." But when the rules were drafted last year, the Consumer Technology Association argued that fees could deter registration.
"Even a small fee — essentially a drone tax — could undermine the FAA's objective of widespread compliance," the organization said in a statement.
It said a fee could ultimately hinder efforts to associate a drone with a single owner.