That’s the thing about our phones, they listen to everything we have to say. That fact alone might drive you nuts, but even if it keeps your conversations private, your phone can learn a lot about you, just by listening to how you speak.

It’s called metadata and there’s a lot of it; who you called and how often, when you called and for how long, your location when you called, and so on. Phone companies and law enforcement have been making use of metadata for a long time; even without recording your conversations, it’s very useful.

But machine learning and artificial intelligence take it a leap further. By listening to your tone of voice, and the speech patterns you unconsciously exhibit, your phone can monitor your stress levels, build up a picture of typical behaviour, and even know if you’re telling the truth.

Combined with physical activity sensors, your phone can monitor your state of mind as well as your state of health, and make some pretty accurate predictions of how you are feeling, as well as how you are likely to behave. Think of it as an analyst or therapist in your pocket!

Knowing in advance that you’re going off the rails can be extremely useful, especially when it’s a health issue that can be positively treated, if diagnosed early enough. But can we trust the app?

E-health services are offloading more and more responsibility to members’ smart devices; they say it’s putting users in control. But the real opportunity is for marketers. “Your personal device now knows more about your emotional state than your own family,” says Annie Archer from Emotion Digital, “and we all know emotion is much more powerful than logic.”

Uh-oh, right now my phone is telling me I’m becoming paranoid – about privacy!