In the EU, it really depends. I think per country, even. It's not as simple as whatever you wrote in the terms gets to hold, or even not as straightforward as equating clicking with accepting.

It's for courts to decide when it gets challenged, but the general idea is, the less obvious or expected the agreement is for normal usage, the less likely it'll hold. So burying some text that amounts to "we get to hack your device" is about as likely to hold as "we get your first born child" (which has been done multiple times by different companies, for fun, and no it doesn't hold).