We all know that our phones can tell advertisers and anyone else who's interested a lot about us, including what websites we've visited and where we've been. I've just about got used to this. But actually our phones can reveal much richer information about us and our surroundings.

A new API now allows web browsers to access information from your phone's ambient light sensor in the camera. Potentially this could be used to map out your home, determine when you go to work, or see if there are other devices are in the same room. 

There are plenty of other sensors on your phone that developers can get access to, all of which genuinely improve the user experience if properly used (the gyroscope is great for a racing game or AR applications) but in malicious hands, and in combination, reveal more than you may be comfortable with.

The challenge for device manufacturers is to give access to more and better sensors to improve the user experience, while ensuring that the door isn't being opened to snooping. Conscious design decisions like restricting outputs to a limited set of states or deliberately adding small amounts of random noise can address this, but maybe we just need to get comfortable that our future will look like Minority Report, with advertisers knowing everything about us.