There are conflicting reports as to the accuracy of this claim, but there's some evidence to suggest that wrapping your phone in tin foil can effectively block any cell signals from reaching it, ultimately making your phone untraceable.

According to It Still Works, the aluminum ultimately disrupts access to your phone's antenna so no calls in or out can be made on the phone as long as it's wrapped.

That being said, some users on Reddit pointed out that if your antenna is located on the outside of your phone, wrapping it in aluminum foil would actually boost its signal, making it easier to send and receive messages and calls. On some of the older iPhones, the lines located on the back of the phone are reportedly the antenna lines. Wrapping some of these phones in tin foil would only increase the cell's signal, rather than suppress it.

We can't confirm for sure whether or not wrapping your phone in aluminum foil will actually block it from being used or traced, as it seems to vary based on the make and model of your phone.