In iOS 9, Apple added a feature called Wifi-Assist that the description says “Automatically use cellular data when Wi-Fi connectivity is poor.” Oh boy! New features! Don’t be so enthused. With the decision to default to having this feature turned on, I’m pretty sure Apple has received a big payoff from wireless carriers. Why? Well, because this “feature” can run your cellphone bill up in a big way (as if you don’t pay enough). Wi-Fi is normally “use as much bandwidth as you want,” whereas cellular data is “pay for each gigabyte you use.”

Here’s a likely scenario a lot of unsuspecting users fall prey to. Let’s say you’re streaming your favorite show from Netflix while you’re connected to wi-fi at your house. You need to go the basement for something, carrying your happily streaming phone with you. The iPhone detects that your wi-fi signal has suddenly dropped to one bar because your router is upstairs on the other side of the house. To keep you from missing precious seconds of your show, it switches from wi-fi to cellular data without giving you any notice. Since you probably don’t have unlimited cellular data, you end up paying big data overage fees, especially if this scenario happens a few times a month (or worse, a few times a day).

My suggestion to most people is to turn this “feature” off. Here’s how:

1. Tap Settings
2. Tap Cellular
3. Scroll all the way down to the bottom of the list (because the carriers don’t want you to turn this off)
4. Toggle the Wi-Fi Assist slider to the off position
5. Use your iPhone without unknowingly running up a huge data bill :)