Apple has sold millions of MacBooks over the years.

But if you own a MacBook Pro, you might not know that the Federal Aviation Administration banned select models of the laptop from aircrafts in August.

The move came shortly after Apple announced that some of the older MacBook Pro units’ batteries posed a fire risk. The restriction was similar to another from 2016, when the FAA banned a Samsung Note 7 model after the mobile device’s battery exploded on several occasions.

Finding out if your model of the world’s most popular laptop is among the those banned is as easy as looking up a serial number on Apple’s recall page. But what happens if you didn’t do that before trying to catch a flight out of Pittsburgh International Airport?

Potentially, the ramifications are serious. Passengers carrying laptops with the recalled batteries (or other hazardous items) “are subject to civil and criminal penalties as appropriate,” according to the FAA’s website.

But the Transportation Security Administration hasn’t cracked down on MacBook owners, perhaps because its officers would significantly delay security lines by checking the serial number of every MacBook passing through security.

TSA spokeswoman Lisa Farbstein referred questions to the FAA.

But when asked about any TSA role in enforcing the ban, an FAA spokeswoman referred comment to the TSA and said passengers bear much of the responsibility.

“The FAA is aware of the recalled batteries that are used in some Apple MacBook Pro laptops. We alerted airlines about the recall, and we informed the public,” the spokeswoman said. “We issued reminders to continue to follow instructions about recalls outlined in the 2016 FAA Safety Alert for Operators and provided information to the public on FAA’s PackSafe website.”

The PackSafe website states that if a product such as a laptop, smart phone or tablet battery is subject to a safety recall, it must not be carried aboard a plane or placed in baggage unless the recalled product component has been replaced, repaired or otherwise made safe per the manufacturer’s instructions.

However, as the FAA acknowledged with the Samsung prohibition in 2016, enforcing bans on electronic devices can be a nearly impossible task.

“It should be noted that it is often difficult to distinguish products that are subject to a recall from those that are not,” the FAA stated at the time.

“Many product recalls only affect certain batches of serial numbers of the same product model. Other recalled products carried by passengers or shipped as cargo may have already been repaired or had the defective lithium batteries replaced. Therefore, active screening methods at the point of acceptance or check-in may be difficult.”