If you need a reminder to turn off the WiFi assist feature included in iOS 9, now’s the time, after yet another report of folks getting hit with data overages because they weren’t aware of what their phones were doing without their knowledge.

In a piece over at The Plain Dealer, Teresa Dixon Murray details how her family’s data usage increased significantly over the course of a few months. Her family shares a 15 GB/month plan, and usually only uses about 10 GB of that allotment. Until recently, when she noticed data usage creeping upward, and their bill took a $30 hit for going over by 1.057 GB.

When she took a closer look at the time stamps for when that data was used, she noticed that in many instances, the family’s phones were getting pinged in the middle of the night, when they were not in use and connected to the home WiFi. Her son’s phone in particular would seek out the cellular network at approximately 12-hour intervals:

Her son went to Verizon to inquire about the weird patterns and was told it could be due to WiFi Assist, a feature that’s turned on by default in iPhones running iOS 9. If it’s on, your phone will automatically use cellular data if WiFi connectivity is weak.

We’ve seen this before, starting in September 2015 upon the release of iOS 9. Shortly after, we heard of an AT&T customer who was charged more than $2,000 in data overages because he didn’t realize WiFi Assist was turned on. Every time his WiFi signal was weak, his phone would turn to the cellular network.

Again, if you don’t want this to happen to you, you can disable the feature by going to Settings –> Cellular and scroll all the way down. The WiFi Assist toggle is at the bottom.

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