By Richard Scott
Personal finance reporter, BBC News
Disclosing your location could reveal other information
How much information do you think your mobile phone company has about you?
Your address, your bank details... what about your religion? Or your sexuality? Does it know if you've been speeding?
Well at the moment, probably not.
But a new report is warning that if we sign up to agreements without reading them properly, this could become a reality.
The Future of Identity in the Information Society, or FIDIS, is an EU funded group where academics are investigating just how much a mobile phone could tell a company about you.
"People don't necessarily realise the amount of information they can give away just by disclosing their location," says Mark Gasson from the University of Reading.
"If we take location as a single point that doesn't necessarily tell you very much but if we collate that information over time then we can actually draw a more detailed picture of the type of person you are."
For this to work, phones have to be the latest generation, with GPS satellite tracking.
Applications on your phone which show where you are, which road to take, or where the nearest petrol station is might be handy, but they could - in theory at least - send all your location information back to the mobile phone company.
The phone companies stress that they take privacy and confidentiality seriously, and do not track people via their mobiles.
But it wouldn't be hard for a company to include a clause in a contract so that when you sign, you're also giving them permission to track where you go - and possibly to even sell this information on.
James Welch, legal director for civil liberties organisation Liberty, argues that people need to be careful: "We all know the temptation to download software without reading the terms and conditions. What this report makes clear is that we all have a responsibility to know what we're signing up for."
Location information is already valuable.
Many haulage companies use it to track their drivers. It lets them tell customers how far away the driver is without having to ring the vehicle - and it's more accurate than a driver simply saying his rough location.
It could also let them divert drivers around traffic problems, or if a driver is accused of reversing into someone's car for example, the system could say whether or not the driver was in that location at the time.
Consumers too could benefit.
By learning your shopping habits, companies could target you with offers that appeal, or let you know about the latest sale, just by tracking which shops you go into.
A GPS phone together with an up to date map will show where you've been and when. In our testing the researchers could name a coffee shop we'd been to for lunch. Although it did wrongly accuse us of also going to the pub.
"If I as a company target you with a cheaper mobile phone... that helps to guide you through the streets, in return I'm getting your location information," points out Tom Ilube from the identity consultants, Garlik.
"I'm getting where you've been, what shops you've been into."
But the applications could be more sinister.
Because it's a real time system, your speed can be calculated - so an insurance company could learn whether you routinely speed on roads for example.
They could also tell how many times you go to the gym, or the pub - which could be used to change your life or health insurance premiums.
A Sunday morning trip to a church would give a good clue as to your religion, and depending on which bars or clubs you visit, a company might be able to guess your sexuality.
Just to be clear - this isn't what happens at the moment.
But today's report is a warning that it could. So it says be careful of what you sign up to, and know your rights over data protection.