Eagle-eyed passengers may have noticed a bizarre bright red strap which goes across the small window in the plane door.
You can watch pilot Harrison Murray (@pilot_geeza) explain its use below:
For what looks to be a pretty random feature - it turns out that there's a good reason why it's there.
The strap usually gets attached to the window as soon as the aircraft starts moving and is removed once it reaches its destination.
Although it looks a bit like a handle, it certainly does not act like one.
So basically, just below the red strap is the big inflatable slide which is automatically inflated in the case of an emergency landing.
Passengers can use the slide to evacuate the aircraft as quickly and safely as possible.
But because the slide inflates almost instantly, it can be quite dangerous.
That's why the red strap is there, to simply act as a sign for the fire brigade.
If the door needs opening from the outside, it's important for the brigade to know if the slide is on or not so it doesn't crush them in the process.
Notably, the red strap is used in Boeing 737 planes and won't be a feature on all of the commercial jets.
Well, just last year an airline passenger was arrested for trying to open the plane door because 'Jesus told her'.
The woman, identified by the courts as Elom Agbegninou, allegedly pushed past a flight attendant and tried to wrench the side door of the aircraft open.
The 34-year-old was detained by a heroic passenger as pilots rerouted to make an emergency landing.
Southwest Airlines said in a statement to LADbible: "Flight 192 traveling from Houston to Columbus safely diverted to Little Rock after our Crew observed disruptive behavior from a passenger on the flight.
"Local authorities in Little Rock met the flight upon landing and removed the Customer from aircraft.
"The flight then departed and landed safely in the original destination of Columbus, Ohio."
The incident began when Agbegninou stood up and made her way to the back of the plane.
Once there, she simply stood and stared intently at the door.
When Agbegninou was told to either use the bathroom or return to her seat by staff, she allegedly refused to do so and asked to look out the window.
The flight attendant and two other staffers declined her request.
The 34-year-old was accused of shoving past and tugging on the handle of the exit door.