If you purchased the latest iPhone or recently updated your old iPhone to iOS 9, there's a default setting you might want to change right away.
In the newest version of Apple's software, there's a new feature called "Wi-Fi Assist."
The feature allows your iPhone to start using your mobile data plan when it detects you have a shaky Wi-Fi connection.
It's a great feature if you have unlimited data because it prevents slow loading on your favorite apps and websites, but many tech blogs point out that it could also quickly eat through limited data plans.
If you don't realize your iPhone is making the switch to mobile data when you're connected to Wi-Fi, you could quickly eat through 2 or 3 GB of data and incur data overage fees.
Those fees can cost you hundreds of dollars on a single bill.
So how do you turn off Wi-Fi Assist?
1. Go to the "Settings" app
2. Open the "Cellular" menu
3. Scroll to the bottom of the screen and disable "Wi-Fi Assist"
Click here to watch how to turn off Wi-Fi Assist